SOLUTION: Need to solve the following x^3+5x^2-4x=20 (hint make sure you set it =0 first)

Question 237876: Need to solve the following
x^3+5x^2-4x=20 (hint make sure you set it =0 first)
Answer by solver91311(24713) (Show Source): You can put this solution on YOUR website!

Standard form:

Rational Root Theorem says that any rational zeros must be of the form

where

is an integer factor of the constant term and

is an integer factor of the lead coefficient.

For this problem the potential rational roots are:

in this case being 1.

Try 1:

No good, has a remainder

Try -1:

No good.

Try 2:

Ok, 2 is a root. That means

is a factor, and from the quotient above we get that

is the other factor.

If you don't understand the synthetic division that I demonstrated above, see http://www.purplemath.com/modules/synthdiv.htm for a very good discussion on the subject. By the way, that is an order, not a suggestion.

Now we know that:

Now all you need to do is factor the quadratic trinomial to get the other two factors and calculate the remaining two roots. Hint: 2 times 5 is 10, 2 plus 5 is 7.

John

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