Examples with solutions for Area of a Triangle: Calculate The Missing Side based on the formula

Exercise #1

The area of triangle ABC is 20 cm².

Its height (AD) is 8.

Calculate the length of the side BC.

S=20S=20S=20888AAACCCBBBDDD

Video Solution

Step-by-Step Solution

We can insert the given data into the formula in order to calculate the area of the triangle:

S=AD×BC2 S=\frac{AD\times BC}{2}

20=8×BC2 20=\frac{8\times BC}{2}

Cross multiplication:

40=8BC 40=8BC

Divide both sides by 8:

408=8BC8 \frac{40}{8}=\frac{8BC}{8}

BC=5 BC=5

Answer

5 cm

Exercise #2

The area of the triangle DEF is 60 cm².

The length of the side FE = 12.

Calculate the height DH.

S=60S=60S=60121212DDDEEEFFFHHH

Video Solution

Step-by-Step Solution

To solve this problem, we'll use the formula for the area of a triangle:

  • Step 1: Write the formula for the area of a triangle: Area=12×base×height \text{Area} = \frac{1}{2} \times \text{base} \times \text{height} .
  • Step 2: Substitute the given values: 60=12×12×DH 60 = \frac{1}{2} \times 12 \times \text{DH} .
  • Step 3: Simplify the equation by calculating the half of the base: 12×12=6 \frac{1}{2} \times 12 = 6 .
  • Step 4: Replace and solve the equation: 60=6×DH 60 = 6 \times \text{DH} .
  • Step 5: Isolate DH\text{DH} by dividing both sides by 6: DH=606 \text{DH} = \frac{60}{6} .
  • Step 6: Calculate the result: DH=10 \text{DH} = 10 .

The height from point D to the base FE, DH \text{DH} , is 10 cm.

Answer

10 cm

Exercise #3

The triangle ABC is a right triangle.

The area of the triangle is 38 cm².

AC = 8

Calculate side BC.

S=38S=38S=38888AAABBBCCC

Video Solution

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Identify the area formula related to a right triangle.
  • Step 2: Set up an equation with the given area and known side.
  • Step 3: Solve for the unknown side BC BC .

Step 1: We know the area A A of a right triangle is given by the formula:
A=12×base×height A = \frac{1}{2} \times \text{base} \times \text{height} .

Step 2: Using the known values, A=38cm2 A = 38 \, \text{cm}^2 , the side AC=8cm \text{AC} = 8 \, \text{cm} and assuming it acts as the base, we set up the equation:
38=12×8×BC 38 = \frac{1}{2} \times 8 \times \text{BC} .

Step 3: Simplify to solve for BC \text{BC} :
Multiply both sides by 2 to eliminate the fraction:
76=8×BC 76 = 8 \times \text{BC} .
Now, divide both sides by 8 to find BC \text{BC} :
BC=768 \text{BC} = \frac{76}{8} .
BC=9.5cm \text{BC} = 9.5 \, \text{cm} .

Therefore, the length of side BC BC is 9.5 cm.

Answer

9.5 cm

Exercise #4

PRS is a triangle.

The length of side SR is 4 cm.
The area of triangle PSR is 30 cm².

Calculate the height PQ.

S=30S=30S=30444PPPRRRSSSQQQ

Video Solution

Step-by-Step Solution

We use the formula to calculate the area of the triangle.

Pay attention: in an obtuse triangle, the height is located outside of the triangle!

SideHeight2=Triangular Area \frac{Side\cdot Height}{2}=\text{Triangular Area}

Double the equation by a common denominator:

4PQ2=30 \frac{4\cdot PQ}{2}=30

2 \cdot2

Divide the equation by the coefficient of PQ PQ .

4PQ=60 4PQ=60 / :4 :4

PQ=15 PQ=15

Answer

15 cm

Exercise #5

The area of triangle DEF is 70 cm².

Calculate h given that the length of side FE is 14 cm.

S=70S=70S=70141414DDDFFFEEE

Video Solution

Step-by-Step Solution

To determine the height h h of triangle DEF given its area is 70 cm² and the side FE is 14 cm, we follow these steps:

  • Identify the known elements: The base b b is 14 cm and the area S S is 70 cm².
  • Use the area formula for a triangle:
    S=12×b×h S = \frac{1}{2} \times b \times h .
  • Rearrange the formula to solve for h h :
    h=2×Sb h = \frac{2 \times S}{b} .
  • Substitute the given values into the formula:
    h=2×7014 h = \frac{2 \times 70}{14} .
  • Simplify the calculation:
    h=14014=10 h = \frac{140}{14} = 10 cm.

Therefore, the height h h of triangle DEF is 10 10 cm.

Answer

10 cm

Exercise #6

ABC is a right triangle with an area of 40.

Calculate the length of side BC.

404040101010AAABBBCCC

Video Solution

Step-by-Step Solution

The problem provides the area of a right triangle ABCABC, which is 40, and tells us that AB=10AB = 10, one of the legs. We need to find the base BCBC of the triangle.

To find BCBC, we use the formula for the area of a triangle:

Area=12×base×height \text{Area} = \frac{1}{2} \times \text{base} \times \text{height}

Here, the area is 40, the height ABAB is 10, and the base is BCBC:

40=12×BC×10 40 = \frac{1}{2} \times BC \times 10

We can simplify this equation to solve for BCBC:

40=5×BC 40 = 5 \times BC
BC=405 BC = \frac{40}{5}
BC=8 BC = 8

Hence, the length of side BCBC is 8 \boxed{8} .

Answer

8

Exercise #7

ABC is a right triangle with an area of 32.

Calculate the length of side BC.

323232888AAABBBCCC

Video Solution

Step-by-Step Solution

To solve this problem, we need to calculate the length of side BC BC in triangle ABC \triangle ABC given that the area is 32 and side AB=8 AB = 8 .

We start by using the area formula for a right triangle:

Area=12×base×height \text{Area} = \frac{1}{2} \times \text{base} \times \text{height}

In this context, the base AB AB is 8, and the height BC BC is the unknown we need to find. Thus, we have:

12×8×BC=32 \frac{1}{2} \times 8 \times BC = 32

We can simplify this equation:

4×BC=32 4 \times BC = 32

Now, solve for BC BC by dividing both sides of the equation by 4:

BC=324=8 BC = \frac{32}{4} = 8

Therefore, the length of side BC BC is 8\mathbf{8}.

Thus, the solution to the problem is BC=8 BC = 8 .

Answer

8

Exercise #8

Look at the right triangle below.

Area = 10

How long is side BC?

101010444AAABBBCCC

Video Solution

Step-by-Step Solution

To find the length of side BC BC , follow these steps:


Step 1: Identify the given information

  • The area of the triangle is given as 10 10 .
  • The height AB AB is 4 4 .


Step 2: Apply the area formula for a right triangle

The formula for the area A A of a triangle is:

A=12×base×height A = \frac{1}{2} \times \text{base} \times \text{height}


Step 3: Set up the equation

Substituting the known values into the formula gives:

10=12×BC×4 10 = \frac{1}{2} \times BC \times 4


Step 4: Solve for BC BC

Begin by simplifying the equation:

10=2×BC 10 = 2 \times BC

Dividing both sides by 2 to solve for BC BC , we obtain:

BC=102=5 BC = \frac{10}{2} = 5


Therefore, the length of side BC BC is 5 5 .

Answer

5

Exercise #9

ABC is a right triangle with an area of 36.

Calculate the length of side BC.

363636121212AAABBBCCC

Video Solution

Step-by-Step Solution

To solve for the length of side BC BC in the right triangle ABC \triangle ABC , we start with the formula for the area of a right triangle:

Area=12×AB×BC\text{Area} = \frac{1}{2} \times AB \times BC

We know the area of the triangle is 36, and the length of side AB AB is 12. We'll substitute these values into the formula:

36=12×12×BC36 = \frac{1}{2} \times 12 \times BC

To isolate BC BC , first multiply both sides of the equation by 2 to eliminate the fraction:

72=12×BC72 = 12 \times BC

Now, solve for BC BC by dividing both sides of the equation by 12:

BC=7212BC = \frac{72}{12}

Upon simplifying, we find:

BC=6BC = 6

Thus, the length of side BC BC is 6\boxed{6}.

Answer

6

Exercise #10

ABC is a right triangle with an area of 21.

Calculate the length of side BC.

212121777AAABBBCCC

Video Solution

Step-by-Step Solution

To solve the problem, we start by identifying that the area of a right triangle is given by the formula:

Area=12×base×height\text{Area} = \frac{1}{2} \times \text{base} \times \text{height}

Given: Area=21 \text{Area} = 21 and one leg of the triangle, say the height AB=7 AB = 7 .

We denote the other leg, which we need to find, as BC BC . Thus:

21=12×7×BC21 = \frac{1}{2} \times 7 \times BC

Solving for BC BC , first multiply both sides by 2 to isolate the product of 7 7 and BC BC :

42=7×BC42 = 7 \times BC

Now, divide both sides by 7 to solve for BC BC :

BC=427=6BC = \frac{42}{7} = 6

Therefore, the length of side BC BC is 6\mathbf{6}.

Answer

6

Exercise #11

A right triangle is shown below.

Its area is 10.5.

Calculate the length of side BC.

10.510.510.5333AAABBBCCC

Video Solution

Step-by-Step Solution

To solve for the length of side BC BC in the right triangle, we will use the area formula for triangles:

  • Step 1: Identify the given elements: Area=10.5 \text{Area} = 10.5 and one leg AB=3 AB = 3 .
  • Step 2: Use the formula for the area of a right triangle:
    Area=12×base×height\text{Area} = \frac{1}{2} \times \text{base} \times \text{height}
  • Step 3: Substitute the known values into the formula:
    10.5=12×3×BC10.5 = \frac{1}{2} \times 3 \times BC
  • Step 4: Solve for BC BC :
    Multiply both sides by 2 to clear the fraction:
    21=3×BC21 = 3 \times BC
  • Step 5: Divide both sides by 3 to isolate BC BC :
    BC=213=7BC = \frac{21}{3} = 7

Therefore, the length of side BC BC is 7 \boxed{7} .

Answer

7

Exercise #12

ABC right triangle with an area of 27.

How long is side BC?

272727999AAABBBCCC

Video Solution

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Use the given information to set up the equation for the area of the triangle.

  • Step 2: Calculate the length of side BC BC using the area formula.

  • Step 3: Verify the solution with the given choices.

Now, let's work through each step:
Step 1: We know the area of the right triangle ABC \triangle ABC is given as 27 27 . The formula for the area of a right triangle is: Area=12×base×height\text{Area} = \frac{1}{2} \times \text{base} \times \text{height}
Given that AB=9 AB = 9 can be considered as the base, let BC BC be the height. Thus, the area formula translates to: 27=12×9×BC 27 = \frac{1}{2} \times 9 \times BC

Step 2: We solve for BC BC by rearranging the formula:
27=12×9×BC 27 = \frac{1}{2} \times 9 \times BC
27=4.5×BC 27 = 4.5 \times BC
BC=274.5 BC = \frac{27}{4.5}
BC=6 BC = 6

Step 3: According to the calculation, the length of BC BC is 6 6 . Reviewing the choices given, the correct answer is option 1: 6 6 .

Therefore, the length of side BC BC is 6 6 .

Answer

6

Exercise #13

ABC is a right triangle with an area of of 7.

Calculate the length of side BC.

777222AAABBBCCC

Video Solution

Step-by-Step Solution

To solve this problem, let's apply the formula for the area of a triangle:

The area A A of a right triangle can be expressed as

A=12×base×height A = \frac{1}{2} \times \text{base} \times \text{height}

Let's denote side BC (the base) as b b and the given height AB as 2. Substituting in the known values, we have:

7=12×b×2 7 = \frac{1}{2} \times b \times 2

Simplifying the right side gives us:

7=b 7 = b

Therefore, the length of side BC is 7 units.

Answer

7

Exercise #14

Calculate X using the data in the figure below.

A=20A=20A=20555XXXAAABBBCCC

Video Solution

Step-by-Step Solution

The formula to calculate the area of a triangle is:

(side * height descending from the side) /2

We place the data we have into the formula to find X:

20=AB×AC2 20=\frac{AB\times AC}{2}

20=x×52 20=\frac{x\times5}{2}

Multiply by 2 to get rid of the fraction:

5x=40 5x=40

Divide both sections by 5:

5x5=405 \frac{5x}{5}=\frac{40}{5}

x=8 x=8

Answer

8

Exercise #15

DEF is a right triangle.

Height GE is 10 cm.
The area of DEF is 40 cm².

Calculate the length of side DF.

S=40S=40S=40101010DDDEEEFFFGGG

Video Solution

Step-by-Step Solution

To solve this problem, we will find the length of side DF using the formula for the area of a triangle:

The area of a triangle is given by:
Area=12×base×height\text{Area} = \frac{1}{2} \times \text{base} \times \text{height}

For triangle DEF, the area is given as 40 cm², and the height GE is 10 cm. We can consider side DF as the base. Therefore, substitute the given values:
12×DF×10=40\frac{1}{2} \times \text{DF} \times 10 = 40

Simplify this expression:
DF×5=40\text{DF} \times 5 = 40

Divide both sides by 5 to solve for DF:
DF=405=8\text{DF} = \frac{40}{5} = 8

Thus, the length of side DF is 8 cm\text{8 cm}.

By comparing with the given choices, the correct answer is indeed choice 1, which is 8 cm.

Therefore, the solution to the problem is 8 cm \text{8 cm} .

Answer

8 cm

Exercise #16

The area of the triangle is 16.

Calculate X.

444xxxAAABBBCCCEEE

Video Solution

Step-by-Step Solution

To solve this problem, we need to find the value of x x , given that the area of the triangle is 16 and the base is known to be 4.

  • Step 1: Identify known values.
    We know the area A=16 A = 16 and base b=4 b = 4 .
  • Step 2: Apply the triangle area formula:
    A=12×b×h A = \frac{1}{2} \times b \times h , where h h is the height we need to calculate.
  • Step 3: Solve for height x x .
    Substitute values into the formula: 16=12×4×x 16 = \frac{1}{2} \times 4 \times x .
  • Step 4: Perform the necessary calculations:
    Simplify the equation: 16=2×x 16 = 2 \times x .
    Divide both sides by 2 to solve for x x .

The calculation simplifies to x=8 x = 8 .

Therefore, the solution to the problem is x=8 x = 8 .

Answer

8

Exercise #17

The area of the triangle is 9.

Calculate X.

333xxxAAABBBCCCEEE

Video Solution

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Identify the given base and area of the triangle.
  • Step 2: Apply the triangle area formula to find the height x x .
  • Step 3: Perform the necessary calculations to determine x x .

Now, let's work through each step:
Step 1: The problem gives us the base BC=3 BC = 3 and the area of the triangle as 9 9 .
Step 2: We'll use the formula Area=12×base×height \text{Area} = \frac{1}{2} \times \text{base} \times \text{height} .
Step 3: Plugging in our values, the equation becomes 9=12×3×x 9 = \frac{1}{2} \times 3 \times x .
Rearranging for x x , we have: x=2×93=183=6 x = \frac{2 \times 9}{3} = \frac{18}{3} = 6 .

Thus, the solution to the problem is x=6 x = 6 .

Answer

6

Exercise #18

The area of the triangle below is equal to 21.

Calculate X.

777xxxAAABBBCCCEEE

Video Solution

Step-by-Step Solution

To solve this problem, let's apply the following steps:

  • Step 1: Identify the formula for the area of a triangle, which is A=12×base×height A = \frac{1}{2} \times \text{base} \times \text{height} .
  • Step 2: Substitute the known values into the formula: 21=12×7×x 21 = \frac{1}{2} \times 7 \times x .
  • Step 3: Simplify and solve the equation for x x .

Now, let's work through each step more precisely:
Step 1: We're given the area formula as A=12×b×h A = \frac{1}{2} \times b \times h .
Step 2: Substitute in the known values: the area A=21 A = 21 , the base b=7 b = 7 , and the height h=x h = x , leading to the equation 21=12×7×x 21 = \frac{1}{2} \times 7 \times x .
Step 3: Solve for x x – first simplify the multiplication on the right: 21=72×x 21 = \frac{7}{2} \times x .
Step 4: To isolate x x , multiply both sides by 2 to get 42=7x 42 = 7x .
Step 5: Finally, divide both sides by 7 to solve for x x : x=427=6 x = \frac{42}{7} = 6 .

Therefore, the value of x x is 6 6 .

Answer

6

Exercise #19

Since the area of the triangle is equal to 15.

Find X.

333xxxAAABBBCCCEEE

Video Solution

Step-by-Step Solution

To solve for x x , let's apply the standard formula for the area of a triangle:

  • Given that the area A=15 A = 15 , base b=3 b = 3 , and height h=x h = x .

The area formula is:

A=12×b×h A = \frac{1}{2} \times b \times h

Substituting the given values into the equation, we have:

15=12×3×x 15 = \frac{1}{2} \times 3 \times x

Now, simplify and solve for x x :

15=32×x 15 = \frac{3}{2} \times x

Multiply both sides by 23 \frac{2}{3} to isolate x x :

x=15×23 x = 15 \times \frac{2}{3}

Calculating, we obtain:

x=303=10 x = \frac{30}{3} = 10

Thus, the height x x of the triangle is x=10 x = 10 .

Therefore, the solution to the problem is x=10 x = 10 .

Answer

10

Exercise #20

The area of the triangle is 12.

Calculate X.

333xxxAAABBBCCCEEE

Video Solution

Step-by-Step Solution

To solve this problem, we'll use the formula for the area of a triangle:

  • Step 1: Identify the given information: Area = 12, base BC=3 BC = 3 , height AE=x AE = x .
  • Step 2: Use the area formula: Area=12×base×height\text{Area} = \frac{1}{2} \times \text{base} \times \text{height}.
  • Step 3: Solve for x x (height) using x=2×Areabase x = \frac{2 \times \text{Area}}{\text{base}} .

Now, substituting the known values into the equation, we get:

x=2×123 x = \frac{2 \times 12}{3}

Performing the multiplication and division yields:

x=243=8 x = \frac{24}{3} = 8

Therefore, the length of x x is 8.

Answer

8