Multiplying two brackets
The question
Spot the mistake: (x + 2)(x + 8) − x² = x² + 10x + 16. Which answer is right?
Spot the mistake: (x + 2)(x + 8) − x² = x² + 10x + 16. Which answer is right?
(x + 2)(x + 8) − x²
(x + 2)(x + 8) − x²=x² + 10x + 16 − x²
(x + 2)(x + 8) − x²=x² + 10x + 16 − x²
(x + 2)(x + 8) − x²=10x + 16
(x + 2)(x + 8) − x²=10x + 16
they wrote:x² + 10x + 16
- Do the step yourself first, then compare with their line.
- On your own, writing every step: (x + 2)(x + 8) − x² becomes x² + 10x + 16 − x².
- Tidy that up and it is 10x + 16.
- Now compare. They wrote x² + 10x + 16, and the x² was never taken away again — so the correct answer is 10x + 16.
How it works.
- 01
Do the step yourself first, then compare with their line.
- 02
On your own, writing every step: (x + 2)(x + 8) − x² becomes x² + 10x + 16 − x².
- 03
Tidy that up and it is 10x + 16.
- 04
Now compare. They wrote x² + 10x + 16, and the x² was never taken away again — so the correct answer is 10x + 16.