Find a side from the area, step by step
If a rectangle covers 48 square centimeters and one side is 6, the other has to be 8 — because 6 times 8 is 48.
The question
cm
Missing side: area 126, one side 18
18 × ? =126
× is undone by ÷
126 ÷ 18 =7 cm
check: 18 × 7 =126
- Forwards, area is one side times the other: 18 × ? = 126. Every number you need is here, which is exactly why the usual mistake is to multiply them.
- But the 126 is the ANSWER to that multiplication, not another side. To get back to the missing one, undo the multiply — and the undo of multiplying is dividing.
- 126 ÷ 18 = 7 cm. Check it forwards: 18 × 7 = 126, which is what the question said.
How it works.
- 01
Forwards, area is one side times the other: 18 × ? = 126. Every number you need is here, which is exactly why the usual mistake is to multiply them.
- 02
But the 126 is the ANSWER to that multiplication, not another side. To get back to the missing one, undo the multiply — and the undo of multiplying is dividing.
- 03
126 ÷ 18 = 7 cm. Check it forwards: 18 × 7 = 126, which is what the question said.