$(x+2)(x-1$)
Totally forgot how to do it. Isn't this the rule:
$(a+b)(c+d)$
$a*c +a*d +b*c +b*d$
The answer I'm getting is $x^2-x+2x-2$ which is wrong. Please help me out, thanks!
$(x+2)(x-1$)
Totally forgot how to do it. Isn't this the rule:
$(a+b)(c+d)$
$a*c +a*d +b*c +b*d$
The answer I'm getting is $x^2-x+2x-2$ which is wrong. Please help me out, thanks!
It's not wrong. You just haven't noticed that $-x+2x = x$, so that, if you simplify, you get $(x+2)(x-1) = x^2 -x + 2x - 2 = x^2 + x - 2.$
The FOIL "rule" (First, Outer, Inner, Last) simply follows from the distributive laws:
$k(m+n) = km + kn$
$(k+m)n = kn + mn$
In your case,
$ \begin{align} (x+2)(x-1) = x(x-1) + 2(x-1) = x^2 - x + 2x - 2 = x^2 + x - 2, \end{align} $
as you have already noted.