Factor by grouping. $$13 x ^ { 2 } + 91 x - 3 x - 21$$
A) $( 13 x - 3 ) ( x + 7 )$
B) $13 x ( x + 7 ) - 3 ( x + 7 )$
C) $13 x ( x + 7 ) - 3 x + 21$
D) $( 13 x - 3 ) ( x - 21 )$
E) $13 x ^ { 2 } + 91 x - 3 ( x + 7 )$

Question

Quizplus · Accepted Answer

We can group the first two terms and the last two terms and factor out the common factor from each group. 
\begin{align*}
13 x ^ { 2 } + 91 x - 3 x - 21 &=(13 x ^ { 2 } + 91 x) - (3 x + 21) \
&= 13x(x+7)-3(x+7)\
&=(13x-3)(x+7)
\end{align*}
Therefore, choice A, $( 13 x - 3 ) ( x + 7 )$, is the correct answer.

Factor by Grouping 13x2+91x−3x−2113 x ^ { 2 } + 91 x - 3 x - 2113x2+91x−3x−21

Factor by Grouping $13 x ^ { 2 } + 91 x - 3 x - 21$