# How do you FOIL (3x - 4)(7x + 7)?

$\left(a + b\right) \left(c + d\right) = a c + a d + b c + b d$
$\left(3 x - 4\right) \left(7 x + 7\right) = 3 x \cdot 7 x + 3 x \cdot 7 - 4 \cdot 7 x - 4 \cdot 7$
(3x-4)(7x+7)=21x²+21x-28x-28
(3x-4)(7x+7)=21x²-7x-28
You can factorize by seven : (3x-4)(7x+7)=7(3x²-x-4)