Sometimes we will need to rearrange a formula to find the value of a subject.
For instance, we may know the area of a circle and need to find the radius. To do this, rearrange the formula to make the radius the subject.
Changing the subject of a formula
The area of a circle (A) is 
r2
So A = r2
If we know the radius, it is easy to find the area using this formula. However, if we know the area and want to find the radius, rearrange the formula to make 'r' the subject.
A = r2
[Start by dividing both sides by pi]
[Then take the square root of both sides]
or
- Question
The formula connecting ºC and ºF is:
Rearrange the formula to make 'F' the subject.
- Answer
[Multiply by 9] 9C = 5(F − 32)
[Divide by 5]
= F − 32[Add 32]
+ 32 = FSo F =
+ 32Note:
is also correct.
- Question
The formula for the volume (V) of a sphere is V = 43
r 3Rearrange the formula to make 'r' the subject.
- Answer
V = 43
r 3[Multiply both sides by 3] 3V = 4
r 3[Divide by 4
]
[Take the cube root of both sides]
Or
Now try a Test Bite
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