The key is to follow the proper order.
First multiply the x on the left times everything in the first parantheses.
(x^3-x) (x+2) +1=0
Next multiply the two parentheses. You have to multiply the first number in the first parentheses (x^3) by everything in the second parentheses, then multiply the second number in the first parentheses by everything in the second parentheses.
Simplify the parentheses by adding and subtracting like terms (x^4 - x^2) and (2x-2x)
Now get the variable alone on one side of the equal sign.
To simplify to x we must find the square root. The square root of (x^2) is x. What we do to one side we must do to the other, so we also have to find the square root of -1. Square roots of negative numbers do not exist so