factor the trinomial completely ........25x^3-55x^2-60x

Question

campbell_st · Answer

take 5x out as a common factor 1st

5x(5x^2 - 11x - 12) 

next factor the trinomial in the brackets.

anonymous · Answer

@campbell_st, how would I do that there are no GCF for 5x^2-11x-12...I'm confused

anonymous · Answer

@campbell_st, how would I do that there are no GCF for 5x^2-11x-12...I'm confused

campbell_st · Answer

here is my method for a trinomial like this

or any quadratic in the form ax^2 + bx + c

multiply a and c        5 x -12 = -60

find the factors of -60 that add to - 11...

campbell_st · Answer

are you able to find the factors..?

anonymous · Answer

give me a sec

anonymous · Answer

10 and 1?

campbell_st · Answer

then it is 

|dw:1352663021174:dw|

you'll find that there are common factors in the numerator that will cancel in the denominator.

campbell_st · Answer

10 x 1 = 10

find 2 numbers that multiply to -60 and add to -11

try  6 x -10  = -60    6 + -10 = -4    not them

     3 x -20 = -60      3 + -20 = -17  not them 

     5 x - 12 = -60      5 + -12 = -7   not them

     any ideas..?

anonymous · Answer

oh multiply ok I missed that some kind of way

anonymous · Answer

ok... I got nothing... I cant think of anything that would be multiplied to get 60 and added to get 11

campbell_st · Answer

well you need something between 3 x -20 and 5 x - 12... any thoughts...?

anonymous · Answer

im sorry..I'm thinking about it

anonymous · Answer

sorry...I have no idea what I'm looking for here...I dont know what's in between 3x-20 and 5x-12.. i just dont get this

campbell_st · Answer

try 4 and - 15.... 

so you have 

|dw:1352663658344:dw|

the solution for the trinomial is done... 

all you need to do is combine the solution.

anonymous · Answer

ok I kind of understand

anonymous · Answer

so first i look for GCF then divide it by that?

anonymous · Answer

what do u mean combine it

campbell_st · Answer

5x(x -3)(5x + 4)