Question

Anna and Belle are asked to solve –2x – 15 = 6x + 9. Identify where one of them made an error.


Anna

Belle


–2x – 15 = 6x + 9
–2x – 15 –6x = 6x + 9 –6x
–8x – 15 = 9
–8x – 15 + 15 = 9 + 15
–8x = 24

x = –3

–2x – 15 = 6x + 9
–2x – 15 + 2x = 6x + 9 + 2x
–15 = 8x + 9
–15 + 9 = 8x + 9 + 9
–6 = 8x

Answer 1

Any ideas?

Answer 2

Hint: Look at these steps
–15 = 8x + 9
–15 + 9 = 8x + 9 + 9 <---how does 9 + 9 = 0
–6 = 8x