Question

Find the zeros of x^3-4x^2-5x=0 please help!!!

Answer 1

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Answer 2

first take out the common factor x:
x(x^2 - 4x - 5) = 0

Answer 3

Ok thaks what do I do next?

Answer 4

now can you factor x^2 - 4x - 5 ?

Answer 5

No. I don't think so.

Answer 6

ok it will factor to 2 binomials of the form
(x + a)(x + b)
in this case a times b will = -5 and a+ b will = -4

Answer 7

so can you figure out what a and b are?

Answer 8

hint: a = -5

Answer 9

(x-5) (x-4)?

Answer 10

no because -4 * -4 = -20 not -5

Answer 11

* -5 * -4 = 20 i meant!

Answer 12

why would you do -5 * -4 though?

Answer 13

the last 2 numbers are multiplied to get the last number

(x - 5)(x - 4) = x*x + x*-4 - 5* x -5*-4
= x^2 - 4x - 5x + 20
= x^2 - 9x + 20
which is nothing like what we require

Answer 14

first x is distributed over the (x - 4) then -5 is distributed over (x - 4)

Answer 15

Oh oh so you FOIL'd it

Answer 16

yes - amounts to same thing

the 2 numbers you require are - 5 and +1
because -5*+1 = -5 and -5+1 = -4

Answer 17

Okay okay thank you. Is that all you do to find the zeros?

Answer 18

well you need to finish the factoring first:
we have
x(x - 5)(x + 1) = 0

so can u find the zeros now?

Answer 19

Would x=5 and x=-1?

Answer 20

thats 2 zeros what about the other?

Answer 21

I'm not sure what to do from there.