How do you multiply #(x + 5)(x - 4)#?

1 Answer
Kuba Dolecki · Stefan V. · George C.
Jul 8, 2015

#x^2 + x - 20#

Explanation:

To multiply two polynomials, you should use the FOIL (first outside inside last) method.

#(x+5)(x-4) = underbrace(x * x)_(color(blue)("first")) + underbrace(x * (-4))_(color(blue)("outside")) + underbrace(5 * x)_(color(blue)("inside")) + underbrace(5 * (-4))_(color(blue)("last"))#

#(x+5)(x-4) = x^2 - 4x + 5x - 20#

Simplify the last equation to get the answer:

#x^2 + x - 20#

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