Homework Help: Algebra

Posted by Adriana on Sunday, October 25, 2009 at 1:05pm.

I distributed 3x^2+x-10=f(x) to find the zeroes. My book's answer was (3x-5)(x+2). When I distributed this to make sure I got the original function, I got 3x^2-x-10. Is this still an acceptable way to factor it even though the x is negative instead of positive as it should be? I got the answers the book got through this method (5/3 and -2) But I don't see how this can be correct with the x being negative.

Algebra - MathMate, Sunday, October 25, 2009 at 4:24pm
Use FOIL
(3x-5)(x+2)
=3x*x + 3x*2 -5*x -5(2)
=3x² + 6x -5x -10
=3x² + x -10
as in the original expresion, and the answer is correct.

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