Question

How do you factor this 8x^2+2x-21=0

Answer 1

$8x^2+2x-21=0 \\ \\ 8x^2+2x + 12x -12x-21=0\\\\8x^2+ 14x -12x-21=0 \\ \\ 2x(4x+7)-3(4x+7)=0\\\\(4x+7)(2x-3)=0$

$4x+7=0 \ \ or \ \ 2x-3 =0 \\\\4x=-7\ \ or \ \ 2x=3\\\\x=\frac{-7}{4}\ \ or \ \ x=\frac{3}{2}$

Answer 2

Solve it like this.. 
8x^2+2x-21=0
8x^2 + 14x - 12x -21=0
2x(4x+7) -3(4x+7) = 0
(4x+7)(2x - 3)=0

So factor 1 is 4x +7 =0 
i.e. x=-7/4

Factor 2 is 2x -3 =0
i.e x=3/2