### Changing the subject of a formula

```Changing the subject
Changing the subject of a formula
When a formula to find a given quantity is written, the
subject of the formula is the letter which is on its own.
Example
A = r2
- Subject A
V=lwh
- Subject V
To change the subject of a formula, we need to re-arrange the
parts of the formula to leave a different letter as the subject.
Remember:
To move any term from one side of the equals sign in a
formula or equation means that the sign is changed.
If there is a choice of terms to be moved we usually move the
However, we cannot always rely on this rule and we just have
to be careful to inspect the equation given.
Make z the subject of the following formula:
1.
Gz = H
H
z =G
2.
8z + T = Y
8z = Y – T
z = Y- T
8
Gxz=H
3.
Lz = Y2 – h
2- h
Y
z= L
Complete Exercise 4 Questions 1 – 30
Formula with x2 and negative x terms
When a formula contains an x2 term that needs to be the
subject we must
• Leave the x2 term on its own first and,
• Then square root the other side to make x the subject.
Example
ax2 = r – t
x2 = r a- t
x = r a- t
When a formula contains a negative x term that is going to be
the new subject
• Move the x term to the other side to make it positive,
• Then make it the subject by leaving it on its own
Example
h – bx = m
h = m + bx
h – m = bx
h-m = x
b
```