Mathematics 7th grade curriculum

1. Rearranging
formulae

2. Content
 What is the subject in math?
 How to change the subject of a formula
 Formula with brackets and fractions

3. Subject
 The subject of a formula is the variable that stands
alone on one side of the formula.
 You can rearrange a formula to make a different
variable the subject.

4. Example
a) 𝑥 = 5𝑦 + 4𝑧 b)𝑠 =
𝑑
𝑡
𝑥 is the subject 𝑠 is the subject

5. To change the subject
To change the subject of a formula you need to ‘undo’
each operation in turn. Use inverse operations.
 Addition is the inverse of subtraction
 Division is the inverse of multiplication.

6. Example
Make 𝑥 the subject of these formulae.
 𝑝𝑞 + 𝑟 = 𝑞 + 𝑥
𝑥 = 𝑝𝑞 + 𝑟 − 𝑞
 𝑚2 = 𝑥 − 𝑛
𝑥 = 𝑚2 + 𝑛

7. Formula with brackets and
fractions
 If there are brackets included in the formula then it is
easier if you expand them first.
 If there are fractions included in the formula then it is
easier if you simplify them first

8. Example
1. 𝑎 𝑥 + 𝑏 = 𝑐
𝑎𝑥 + 𝑎𝑏 = 𝑐
2.
𝑥
𝑎
= 1 +
𝑦
𝑏
𝑏𝑥 = 𝑎𝑏 + 𝑎𝑦

9. Questions
 Using 𝑃 = 2(𝑥 − 3) change the subject of the formula
to 𝑥.
 Change the subject of the formula 𝐸𝑘 =
1
2
𝑚𝑣2 to 𝑣.
 Using the formula for the area of a circle, change the
subject of the formula to “𝑟”