SOLUTION: factor the pollynomial completely x3+5x2-8x-40

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Question 189976: factor the pollynomial completely
x3+5x2-8x-40
Found 2 solutions by nerdybill, Alan3354:
Answer by nerdybill(7384) About Me  (Show Source):
You can put this solution on YOUR website!
Factor by "grouping":
x^3+5x^2-8x-40
= (x^3+5x^2)-(8x+40)
= x^2(x+5)-8(x+5)
= (x+5)(x^2-8)

Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
factor the pollynomial completely
x3+5x2-8x-40
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In a classroom, these are always integers.
Look at the 40 - a zero will be a factor of 40.
Try (+ and minus) 1, 2, 4 and 5. f(-5) = 0, so (x+5) is a factor.
Once you divide by (x+5), it's only a 2nd order, easy to factor further, if possible.
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Another approach is to graph the function and look for zeroes.
dl the free software at
www.padowan.dk.com/graph/