Question

Can someone help me factor 5k^3+20k^2-15

Answer 1

first find the GCF of the 3 terms
it must be a number because of the 15 at the end

so what's the greatest common factor of 5, 15 and 20 ?

Answer 2

5, right

Answer 3

yes to take 5 out and u can write:

5(k^3 + 4k^2 - 3)

Answer 4

So, to factor stuff you just take out the GCF?

Answer 5

well sometimes

Answer 6

its the first thing you look for

Answer 7

ok, is there anything else i need to do?

Answer 8

no - thats it

Answer 9

ok thanks :)

Answer 10

Well, wait a minute
\[
5 k^3+20 k^2-15=5 (k+1) \left(k^2+3
k-3\right)
\]

Answer 11

http://www.wolframalpha.com/input/?i=factor+5+k^3%2B20+k^2-15+

Answer 12

oh yes - i missed that - sorry Jailee

Answer 13

its fine thanks again

Answer 14

yw - these cubic expressions can sometimes be factored

Answer 15

for a cubic try to find a zero by hit and trial method.
try k=-1
5(-1)^3+20(-1)^2-15=-5+20-15=0
hence k=-1 or k+1 is a factor
divide by -1,for synthetic division or by k+1 long division.
you get other factor.