Question 652348: 91z+30z^2-30 factored completely
Answer by Shana-D77(132)   (Show Source):
You can put this solution on YOUR website! It's best to rearrange this to 30z^2 + 91z - 30 (Az^2 + Bz + C)
First, multiply A*C (30*-30 = 900)
Ask "What two numbers multiply to get -900 that add to get B (91)?"
Answer: 100*-9 (trial and error)
Rewrite B using the pair you just found:
30z^2 + 91z - 30
30z^2 + 100z - 9z - 30
Parenthesize:
(30z^2 + 100z) - (9z - 30)
Factor each parenthesis:
10z(3z + 10) - 3(3z + 10) <<- the parenthesis will always be the same. The first one is always right.
Rewrite: One () is the stuff on the inside once, the other () is the stuff on the outside:
(3z + 10)(10z - 3)
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