Question

Which of the following represents the zeros of f(x) = x3 − 4x2 − 5x + 20?

Answer 1

f(x) = 0

x-axis intercepts

Answer 2

looks like one of those where you can regroup things, and factor it

Answer 3

the choices are

−4, −square root of 5, −square root of 5
4, square root of 5, −square root of 5
4, −square root of 5, −square root of 5
−4, square root of 5, square root of 5

Answer 4

i don't understand how to get to those

Answer 5

[x^3 - 5x] - 4x^2 + 20

both of those pairs have a common factor

x*(x^2 - 5) - 4 * (x^2 - 5)

Answer 6

so you can then factor that now, take x^2 -5 from both


=

(x^2 - 5) * ( x - 4 )

Answer 7

what do I do after that? @DanJS

Answer 8

That is it.

Answer 9

The answer is:

\[(x^2-5)(x-4)\]

and @DanJS Is now offline.

Answer 10

Hope this helped! Have a great day!

Also a medal would be much appreciated! Just click best response next to my answer. Thank You!

@madmerc

Answer 11

@AihberKhan that isn't one of the choices though..

Answer 12

The answer was
4, square root of 5, −square root of 5

Answer 13

hint:
use identity: a^2-b^2=(a+b)(a-b).
So if \((x^2-7)=0\), we have
\((x^2-(\sqrt 7)^2)=(x+\sqrt 7)(x-\sqrt 7)=0 ~~~=>~~~ x=\sqrt 7~or~ x=-\sqrt 7\)