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How do you find all zeros of #y=x^3+x^2-9x-9#?

1 Answer

May 12, 2015

Set #y=0# and solve for #x#:
#x^3+x^2-9x-9=0#

Collecting #x# from the first and third term:
#x(x^2-9)+x^2-9=0#
#(x^2-9)(x+1)=0#
So:

#x^2-9=0#
#x=+-sqrt(9)=+-3#
and

#x+1=0#

Giving:
#x_1=3#
#x_2=-3#
#x_3=-1#

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