Examples with solutions for Area of a Triangle: Using variables

Exercise #1

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 #2

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 #3

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 #4

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 #5

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

Exercise #6

Since the area of the triangle is equal to 15.

Find X.

555xxxAAABBBCCCEEE

Video Solution

Step-by-Step Solution

To find x x , the vertical height of the triangle, we will use the area formula for a triangle:

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

We know that:

  • The area of the triangle is 15.
  • The base of the triangle, BE BE , is 5 units.
  • The height of the triangle, AE AE , is x x units.

Substituting these values into the formula, we get:

15=12×5×x 15 = \frac{1}{2} \times 5 \times x

First, simplify the right side of the equation:

15=52×x 15 = \frac{5}{2} \times x

To isolate x x , multiply both sides by 2:

30=5x 30 = 5x

Finally, divide both sides by 5 to solve for x x :

x=305=6 x = \frac{30}{5} = 6

Therefore, the value of x x is 6.

Answer

6

Exercise #7

The area of the triangle below is equal to 3.

Calculate X.

222xxxAAABBBCCCEEE

Video Solution

Step-by-Step Solution

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

  • Step 1: Identify the given information.
  • Step 2: Apply the formula for the area of a triangle.
  • Step 3: Solve for X X .

Now, let's work through each step:
Step 1: The problem provides the area of the triangle as 3 3 square units, with the base of the triangle as 2 2 units.
Step 2: The formula used for the area of a triangle is Area=12×base×height\text{Area} = \frac{1}{2} \times \text{base} \times \text{height}.
Given that the base is 2 2 and the area is 3 3 , we rearrange to find X X (the height):

3=12×2×X 3 = \frac{1}{2} \times 2 \times X

Simplifying, we get:

3=X 3 = X

Therefore, the length of X X is 3 3 .

Answer

3

Exercise #8

The area of the triangle is equal to 18.

Calculate X.

666xxxAAABBBCCCEEE

Video Solution

Step-by-Step Solution

To solve for x x , we begin by applying the formula for the area of a triangle:

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

Given: the area is 18, AE is the height (6) , and EC is the x.

Insert the known values into the formula:

18=12×6×x 18 = \frac{1}{2} \times 6 \times x

Simplify the equation:

18=3x 18 = 3x

Next, solve for x x by dividing both sides by 3:

x=183 x = \frac{18}{3}

Calculate:

x=6 x = 6

Thus, the length x x is 6 \mathbf{6} .

Answer

6

Exercise #9

Look at the triangle ABC below.

BC = 6

AD = X

Express the area of the triangle using X.

666XXXCCCAAABBBDDD

Video Solution

Step-by-Step Solution

To express the area of triangle ABC \triangle ABC using X X , follow these steps:

  • Identify the base BC=6 BC = 6 .
  • Identify the height as AD=X AD = X .
  • Use the formula for the area of a triangle: Area=12×base×height \text{Area} = \frac{1}{2} \times \text{base} \times \text{height} .
  • Substitute the known values: Area=12×6×X \text{Area} = \frac{1}{2} \times 6 \times X .
  • Simplify the expression: Area=6X2 \text{Area} = \frac{6X}{2} .
  • Further simplify: Area=3X \text{Area} = 3X .

Comparing this with the choices given, choices B (6X2 \frac{6X}{2} ) and C (3X 3X ) are both valid representations of the area.

Therefore, the correct answer is that choices B and C are correct.

Answers B and C are correct.

Answer

Answers B and C are correct.

Exercise #10

Given the rectangle ABCD

Given BC=X and the side AB is larger by 4 cm than the side BC.

The area of the triangle ABC is 8X cm².

What is the area of the rectangle?

S=8XS=8XS=8XX+4X+4X+4XXXAAABBBCCCDDD

Video Solution

Step-by-Step Solution

Let's calculate the area of triangle ABC:

8x=(x+4)x2 8x=\frac{(x+4)x}{2}

Multiply by 2:

16x=(x+4)x 16x=(x+4)x

Divide by x:

16=x+4 16=x+4

Let's move 4 to the left side and change the sign accordingly:

164=x 16-4=x

12=x 12=x

Now let's calculate the area of the rectangle, multiply the length and width where BC equals 12 and AB equals 16:

16×12=192 16\times12=192

Answer

192

Exercise #11

Calculate X using the data in the figure below.

A=22.5A=22.5A=22.5X+6X+6X+6555AAABBBCCC

Video Solution

Answer

3

Exercise #12

Express the area of the triangle ABC in terms of X.

2X2X2XAAABBBCCCDDD8X+1

Video Solution

Answer

X+923X22X1 \frac{X+9}{2}\sqrt{3X^2-2X-1}