Question

Find the error(s) and solve the problem correctly.

Sarah was asked to solve the following problem. Identify her errors and explain how to correct her mistakes.

Answer 1

5x^3-18^2 +2x +21

Explanation:

Answer 2

`5x^3-18x^2+2x+21`

Explanation:

In the second step, -9x-21 should be 9x+21. This is because -3 in x-3, and -3x-7 in 5x²-3x-7 are both negative, so each term's product should be positive.

Also, in the third line, she wrote -3x²-15x² as -18x⁴ instead of -18x²,and similarly, she wrote -7x-9x as -16x² (however this is wrong anyway because step 2 was done incorrectly).

If we continued off from the second step with these corrected errors:

`5x^3-3x^2-7x-15x^2+9x+21\\5x^3-18x^2+2x+21`

Therefore, the correct simplification is
`5x^3-18x^2+2x+21`.