1 identify the error in the solved problem 2 correctly solve

1 identify the error in the solved problem
2 correctly solve/simplify the problem showing steps
3 write a few sentences explaining how to avoid this mistake

Solution

f(x+1)=(x+1)²+8(x+1)-8 but in the solved problem -8 is printed as +8

f(x+1)=x²+2x+1+8x+8-8

f(x+1)=x²+10x+1