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October 21, 2014

October 21, 2014

Posted by **anon** on Friday, December 9, 2011 at 4:36pm.

x^3 + 8x^2 + 10x - 15 = 0

Please help me!

- algebra -
**Steve**, Friday, December 9, 2011 at 5:21pmSince it is hard to factor a general cubic, look for easy roots. They will be among ±1,3,5,15

A little synthetic division shows that we have

(x+3)(x^2 + 5x - 5)

Now you can use the quadratic formula to get the other two roots:

(-5 ± 3√5)/2

- algebra -
**bobpursley**, Friday, December 9, 2011 at 5:26pmby inspection, x=-3 is a solution.

-27+72-30-15=0

so, divide (x+3) into x^3+8x^2+10x-15 and get the quadratic. Then solve it with the quadratic equation.

I get x^2+5x-5 check that.

- algebra -
**sue**, Friday, December 9, 2011 at 10:02pmThank you I think I understand it better with Bob's answer.

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