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Finding the Shorter Side Using Pythagoras' Theorem

In this worksheet, students will learn how to find the shorter side length of a right angled triangle using Pythagoras' Theorem.

'Finding the Shorter Side Using Pythagoras' Theorem' worksheet

Key stage:  KS 4

GCSE Subjects:   Maths

GCSE Boards:   AQA, Eduqas, Pearson Edexcel, OCR,

Curriculum topic:   Geometry and Measures, Mensuration

Curriculum subtopic:   Mensuration and Calculation Triangle Mensuration

Difficulty level:  

Worksheet Overview

You should be confident at recalling Pythagoras' theorem:

 

right triangle abc

 

a² + b² = c² 

a and b are the shorter sides of a right angled triangle and c is the hypotenuse.

Sometimes you will need to find a shorter side, so this will require you to rearrange the formula.

Rearranging for a gives:

a = √(c² - b²)

Substituting lengths c and b into the formula will instantly find the shorter side.

Let's take a look at an example:

Find length a of this triangle.

 

c=16, b=11, a=x

 

The formula gives:

a = √(c² - b²) = 11.62 (to 2 decimal places).

 
If the formula appears confusing, we can break it down and solve it in these three steps:

1.  Square both sides.
16 x 16 = 256
11 x 11 = 121

2. Subtract your answers
256 - 121 = 135

3. Square root
√135 = 11.62 (to 2 decimal places).

 

 

Think of it this way: "square, square, subtract, square root".

Remember: if it is the shorter side you want to find, your answer will never be larger than the length of the hypotenuse.

This is a good way to evaluate whether your answer is correct.  It is always important to check.

 

Now that you have seen the formula and the method, write it down and test your understanding with this activity.

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