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

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

x^2 + x - 20x2+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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