algebra

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solve the following in the real number system
x^3 + 8x^2 + 10x - 15 = 0
Please help me!

  • algebra -

    Since 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 -

    by 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 -

    Thank you I think I understand it better with Bob's answer.

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