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how do you find zeros of x^3-4x^2-25x-100?
Find it without a calculator*
I know you could group so it becomes:
x^2(x-4) - 25(x+4)
but I don't know what to do from there because x-4 and x+4 are different so i can't use a common factor....or can i? do the signs not matter?
anyway, regardless of the method (as long as it's by hand, not calculator), can someone explain it to me?
thanks
holy crap....I'm so mad. i checked my teacher's answer key online- her equation is +100 while on the student worksheet online the equation is -100....i spent like 20 minutes going over this problem... D:
argh but thanks for the help :].
1 Answer
- Roger the MoleLv 71 decade agoFavorite Answer
You are right to think of factoring by grouping, but you are also correct to notice that it doesn't quite work.
As written, your equation has one complicated irrational root and two complicated irrational complex roots, which makes me think the problem has been copied incorrectly.
It would have been much nicer if it had been
x^3 - 4x^2 - 25x + 100
which has three real roots.
