factor the trinomial completely
4u^2+4u-15

Question

factor the trinomial completely 
4u^2+4u-15

hartnn · Answer

tried this ?

vortish · Answer

i do not think this can be factored i think it is a prime

vortish · Answer

i does not make sense 4 can not be factored in t o15

hartnn · Answer

how you could conclude that ? did you find out the value of determinant b^2-4ac ?

hartnn · Answer

actually you need to find 2 numbers with product 4*(-15)=60 and sum 4

hartnn · Answer

4*(-15)=-60

vortish · Answer

so what your saying i have to find a number that -60 will = 4

hartnn · Answer

2 numbers whose product is -60 and whose sum is 4
(here, one number is negative)

vortish · Answer

-1086=-60  10*-6=-60 10-6=4

hartnn · Answer

-1086 ??
10 and -6 are correct,
so split +4u into 10u-6u
now try...

hartnn · Answer

ohh, 10 & 6

vortish · Answer

(u+10)(u-6)

hartnn · Answer

huh ? no...
4u^2 +10u -6u -15 =0
factor out 2u from 1st 2 terms and -3 from last 2 terms, what u get ?

vortish · Answer

2u+4u -5

hartnn · Answer

??
(4u^2 +10u) + (-6u -15) =0
2u (2u+5) -3 (2u+5) =0
got this ?

vortish · Answer

yes sir

hartnn · Answer

now factor out 2u+5 from that

vortish · Answer

(2u-3)=0

hartnn · Answer

2u+5 just disappeared :O :P 
(2u+5)(2u-3) is your factored form :)

vortish · Answer

so you can only factor out one of the (2u+5) out of the expression

vortish · Answer

so the final answer would be (2u+5)(2u-3)

hartnn · Answer

its like ab+ac = a(b+c)
(2u+5)*2u + (2u+5)*(-3) = (2u+5)(2u-3)
and yes.

vortish · Answer

ok thank you sir

hartnn · Answer

welcome ^_^