Can #y=x^3+8x^2+17x+10# be factored? If so what are the factors ?

1 Answer
Jan 6, 2016

Yes, it can.
#y=(x+1)(x+2)(x+5)#

Explanation:

To factorize a n-degree-polynomial function, one must discover its roots that will allow to rearrange the function in this way
#f(x)=(x-x_1)(x-x_2)[...]"(x-x_n)#

For a polynomial of the third degree, when all coefficients are real numbers, there's at least one real root. The other two roots are either real numbers or complex conjugate numbers.

For a general solution of roots of the third degree equation, requiring some ability to work with complex numbers, I recommend this source:
Roots of a cubic function

But we can try to resolve the problem the easy way.

The coefficient d may help us to find at least one real root.
#d=18=2*5#
This is why we should try the possible roots #+-1, +-2, +-10# and also #+-1/2, +-1/5 and +-1/10##.

Luckily #x_1=-1# is a root of the function:
#f(x=-1)=-1+8-17+10=0#

Then we should divide the polynomial by #(x-x_1)=(x+1)#:
#" "x^3+8x^2+17x+10" "#|#" "x+1#
#-x^3-x^2" "#|____
___#" "x^2+7x+10#
#" "7x^2+17x#
#" "-7x^2 -7x#
#" "#
__
#" "10x+10#
#" "-10x-10#
#" "#
_____
#" "0#

The second degree factor can still be further factorized:
#x^2+7x+10=0#
#Delta=49-40=9#
#x=(-7+-sqrt(9))/2# => #x_2=-2#; #x_3=-5#

Then the function factorized is
#f(x)=(x-x_1)(x-x_2)(x-x_3)=(x-1)(x-2)(x-5)#