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A cubic function y has real coefficients, and its zeros are 5, -4 and 1. If x=-3, y=64 satisfies its equation, find the equation of the cubic function in standard form.

 Nov 1, 2020
edited by xxJenny1213xx  Nov 1, 2020
 #1
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(x-5)(x+4)(x-1) = 0      subbing in x = -3   yields   32    so there must be a 2 multiplier

2 (x-5)(x+4)(x-1) =    multiply all of this out :

2x^3-4x^2-38x+40

 Nov 1, 2020
 #2
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Guest is correct 

But maybe this will explain better where the 2 came from.

 

\(y=a(x-5)(x+4)(x-1)\)

 

just sub in x=-3 and y=64 

Solve for a

 

And yes you do have to expand it.

 Nov 1, 2020
 #3
avatar+346 
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thank you.

xxJenny1213xx  Nov 2, 2020

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