Question 144219: can someone tell me the answer to
factor: 3x2-19x-40 (i think you'd say 3xsquared(the 2 is up higher)
and
factor: 9x2-12x+4 (i think you'd say 3xsquared(the 2 is up higher)
i've been trying for hours, i just don't get it and it's 3am and i need to be up in 3 hours
Answer by ankor@dixie-net.com(22740)   (Show Source):
You can put this solution on YOUR website! 3x^2 - 19x - 40
:
First write it:
(3x ___)(x ___)
:
You know the values in the blanks will be factors of -40,
(one will be neg, the other positive):
1, 40
2, 20
4, 10
5, 8
Because the middle term is neg, the larger factor has to be negative
:
FOIL these values until you get the given expression:
:
(3x + 5)(x - 8) FOILs to 3x^2 - 24x + 5x - 40 which is:
:
3x^2 - 19x - 40
FOIL these values until the
:
:
factor: 9x^2 - 12x + 4
:
The clue on this one is that both the coefficient of x (9) and 4 are perfect squares.
Try these values first.
:
Since the middle term is neg and the 3rd terms is positive it must be:
(3x - 2)(3x - 2) or (3x-2)^2
:
FOIL this and you get the original expression:
9x^2 - 6x - 6x + 4 = 9x^2 - 12x + 4
:
Practice doing these and it will become pretty easy.
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