Correct the error then solve

Question

(x³ - 8x + 2) + (3x³ + 7x + 6)

x³ - 8x + 2 + 3x³ + 7x + 6

(x³ + 3x³) - (8x + 7x) + (2 + 6)

4x³ - 15 + 8

Answer 1

The middle term on the 3rd row is wrong. Since there is a negative in front of the parentheses, it makes the +7x into a -7x which is not what row 2 says. You need to change that +7x into a -7x and get the correct answer 4x³-x+8. Note that the last row is also wrong, in that it is missing the x from the middle term. ■