SOLUTION: I need to factor this out by trial-and-error.... (D) 40x^2+7x-20 Can you plz explain step by step so I understand what your doing...thnx.

Question 439399: I need to factor this out by trial-and-error....
(D) 40x^2+7x-20

Can you plz explain step by step so I understand what your doing...thnx.
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
40x^2+7x-20
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Use Inverse FOIL:
Find two numbers whose
product is 40*-20 = -800
and whose sum is +7
----
The numbers are 32 and -25
--------------------------------
= 40x^2 +32x-25x -20
----
= 8x(5x+4) -5(5x+4)
----
Factor:
= (5x+4)(8x-5)
======================
Cheers,
Stan H.
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