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What are the zeros of f(x)=x^2+x-20? A.x=-2 and x=10 B.x=-10 and x=2 C.x=-5 and x=4 D.x=-4 and x=5
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What are the zeros of f(x)=x^2+x-20?

A.x=-2 and x=10
B.x=-10 and x=2
C.x=-5 and x=4
D.x=-4 and x=5

User Earcam
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1 Answer

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f(x) = x² + x - 20 = x² + 5x - 4x - 20 = x(x + 5) - 4(x + 5) = (x + 5)(x - 4)

f(x) = 0 ⇔ (x + 5)(x - 4) = 0 ⇔ x + 5 = 0 or x - 4 = 0 ⇒ x = -5 or x = 4

Answer: C. x = -5 and x = 4.
User Jukempff
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