Examples with solutions for Using the Pythagorean Theorem: Calculate The Missing Side based on the formula

Exercise #1

Given the triangle ABC, find the length BC

131313555AAACCCBBB

Video Solution

Step-by-Step Solution

To answer this question, we must know the Pythagorean Theorem

The theorem allows us to calculate the sides of a right triangle.

We identify the sides:

ab = a = 5
bc = b = ?

ac = c = 13

 

We replace the data in the exercise:

5²+?² = 13²

We swap the sections

?²=13²-5²

?²=169-25

?²=144

?=12

Answer

12 cm

Exercise #2

Look at the triangle in the diagram. How long is side BC?

222777AAABBBCCC

Video Solution

Step-by-Step Solution

To solve the exercise, it is necessary to know the Pythagorean Theorem:

A²+B²=C²

We replace the known data:

2²+B²=7²

4+B²=49

We input into the formula:

B²=49-4

B²=45

We find the root

B=√45

This is the solution. However, we can simplify the root a bit more.

First, let's break it down into prime numbers:

B=√(9*5)

We use the property of roots in multiplication:

B=√9*√5

B=3√5

This is the solution!

Answer

35 3\sqrt{5} cm

Exercise #3

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What is the length of the side marked X?

Video Solution

Step-by-Step Solution

We use the Pythagorean theorem:

AB2+BC2=AC2 AB^2+BC^2=AC^2

Answer

15 15

Exercise #4

AAABBBCCCDDD2524Calculate the perimeter of the rectangle ABCD.

Video Solution

Step-by-Step Solution

Let's focus on triangle BCD in order to find side BC.

We'll use the Pythagorean theorem using our values:

BC2+DC2=BD2 BC^2+DC^2=BD^2

BC2+242=252 BC^2+24^2=25^2

BC2=625576=49 BC^2=625-576=49

Let's now remove the square root:

BC=7 BC=7

Since each pair of opposite sides are equal to each other in a rectangle, we can state that:

DC=AB=24 DC=AB=24

BC=AD=7 BC=AD=7

Now we can calculate the perimeter of the rectangle by adding all sides together:

24+7+24+7=14+48=62 24+7+24+7=14+48=62

Answer

62

Exercise #5

Look at the following rectangle:

AAABBBCCCDDD1312

AB = 12

AC = 13

Calculate the area of the triangle BCD.

Video Solution

Step-by-Step Solution

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

  • Step 1: Use the Pythagorean Theorem to calculate the length of AD AD .
  • Step 2: Calculate the area of triangle BCD \triangle BCD .

Step 1: Given AB=12 AB = 12 and AC=13 AC = 13 , we use the Pythagorean Theorem to find AD AD .

AC2=AB2+AD2    132=122+AD2 AC^2 = AB^2 + AD^2 \implies 13^2 = 12^2 + AD^2 169=144+AD2    AD2=25    AD=5 169 = 144 + AD^2 \implies AD^2 = 25 \implies AD = 5

Step 2: Knowing the sides AD=5 AD = 5 (height of the rectangle) and AB=12 AB = 12 (base of the rectangle), triangle BCD \triangle BCD will have the base BC=12 BC = 12 and the height BD=5 BD = 5 .

The area of triangle BCD \triangle BCD is:

AreaBCD=12×base×height=12×12×5=30 \text{Area}_{\triangle BCD} = \frac{1}{2} \times \text{base} \times \text{height} = \frac{1}{2} \times 12 \times 5 = 30

Therefore, the area of triangle BCD \triangle BCD is 30.

Answer

30

Exercise #6

Look at the triangle in the figure.

What is the length of the hypotenuse given that its perimeter is 12+45 12+4\sqrt{5} cm?

444AAABBBCCC

Video Solution

Step-by-Step Solution

We calculate the perimeter of the triangle:

12+45=4+AC+BC 12+4\sqrt{5}=4+AC+BC

As we want to find the hypotenuse (BC), we isolate it:

12+454AC=BC 12+4\sqrt{5}-4-AC=BC

BC=8+45AC BC=8+4\sqrt{5}-AC

Then calculate AC using the Pythagorean theorem:

AB2+AC2=BC2 AB^2+AC^2=BC^2

42+AC2=(8+45AC)2 4^2+AC^2=(8+4\sqrt{5}-AC)^2

16+AC2=(8+45)22×AC(8+45)+AC2 16+AC^2=(8+4\sqrt{5})^2-2\times AC(8+4\sqrt{5})+AC^2

We then simplify the two:AC2 AC^2

16=82+2×8×45+(45)22×8×AC2AC45 16=8^2+2\times8\times4\sqrt{5}+(4\sqrt{5})^2-2\times8\times AC-2AC4\sqrt{5}

16=64+645+16×516AC85AC 16=64+64\sqrt{5}+16\times5-16AC-8\sqrt{5}AC

16AC+85AC=64+645+16×516 16AC+8\sqrt{5}AC=64+64\sqrt{5}+16\times5-16

AC(16+85)=128+645 AC(16+8\sqrt{5})=128+64\sqrt{5}

AC=128+64516+85=8(16+85)16+85 AC=\frac{128+64\sqrt{5}}{16+8\sqrt{5}}=\frac{8(16+8\sqrt{5})}{16+8\sqrt{5}}

We simplify to obtain:

AC=8 AC=8

Now we can replace AC with the value we found for BC:

BC=8+45AC BC=8+4\sqrt{5}-AC

BC=8+458=45 BC=8+4\sqrt{5}-8=4\sqrt{5}

Answer

45 4\sqrt{5} cm