Question 83861
y^4+3y^3-5y^2-15y
Factor out the "y" factor:

=y(y^3+3y^2-5y-15)
Factor the 1st two and the last two terms separately to get:

=y(y^2(y+3)-5(y+3))
Factor out the "y+3" factor

=y(y+3)(y^2-5)
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Cheers,
Stan H.