Some equations need two steps. In 4x − 5 = 7, x is multiplied by 4 and then 5 is taken away. To undo this, work backwards: first add 5 to both sides, then divide by 4.
4x − 5 = 7 becomes 4x = 12, then x = 3. The order matters: undo the adding or subtracting first, then the multiplying or dividing. A balance picture helps: the scales stay level only if you do the same to both sides.
Worked example
Solve 3x + 9 = 15
- Subtract 9 from both sides: 3x = 6.
- Divide both sides by 3.
Answer:x = 2
Key words
- two-step equation
- an equation that needs two inverse operations
- balance
- keeping both sides equal
- coefficient
- the number in front of x
Practise this
New questions every time.
Common Core-referenced: 7.EE.B.4a