Factor by grouping.
-$$4 x ^ { 2 } - 20 x - 28 x + 140$$
A) $( x - 5 ) ( 4 x - 28 )$
B) $4 ( x + 5 ) ( x + 7 )$
C) $4 ( x - 5 ) ( x - 7 )$
D) $( x - 5 ) ( x - 7 )$

Question

Quizplus · Accepted Answer

Group the first two terms and the last two terms: 
$$(4x^2-20x) + (-28x+140)$$ 
Factor out a common factor from each group: 
$$4x(x-5)-28(x-5)$$ 
Notice that there is now a common factor of $(x-5)$, so factor it out: 
$$(x-5)(4x-28)$$ 
Simplify: 
$$(x-5)(4(x-7)) = 4(x-5)(x-7)$$ 
The correct answer is C, which is equivalent to the simplified form of the factored expression.

Factor by Grouping 4x2−20x−28x+1404 x ^ { 2 } - 20 x - 28 x + 1404x2−20x−28x+140

Factor by Grouping $4 x ^ { 2 } - 20 x - 28 x + 140$