1. Changing the subject of a formula
Thursday, 17 January 2019
Changing the subject of a formula
The formula for the area of a rectangle is:
Area = Length X Width
A = L X W
A = LW
The letter a the front is called the SUBJECT of the formula

2. Area = 15 (cm2) Area = Length X Width A = L X W A = LW Length = 5 (cm)
What is the width?
Length = 5 (cm)
A = L X W
15 = 5 X W
15 = 5 X 3
So the width is 3 (cm)

3. To find the width, I divided 15 by 5
Area = 15 (cm2)
How did you do that?
To find the width, I divided 15 by 5
15 ÷ 5 = 3
Length = 5 (cm)
W = Area ÷ Length
W = A ÷ L
W = A/L
A = L X W
A = LW

4. Another formula can be found for the LENGTH
Area = 15 (cm2)
Width = 3 (cm)
A = L X W
A = LW
Length = 5 (cm)
W = Area ÷ Length
W = A ÷ L
W = A/L
L = Area ÷ Width
L = A ÷ W
L = A/W

5. Here are the three formulae for a rectangle
A is the subject
A = L X W
A = LW
W is the subject
L is the subject
W = Area ÷ Length
W = A ÷ L
W = A/L
L = Area ÷ Width
L = A ÷ W
L = A/W