Question 520175: x^2-9x-36=0 solve for x
Answer by jessica43(140)   (Show Source):
You can put this solution on YOUR website! To solve this problem you need to factor the trinomial, which is the opposite of the FOIL method. The factors will have this form:
(x A)(x B)
where A and B will be the factors of the third term (-36). The factors of -36 are: -1, 1, -2,2,-3, 3,-4, 4,-6,6 -9, 9, -12, 12,-18, 18, -36 and -36. So these are our possibilities of A and B: -1&36, 1&-36, -2&18, 2&-18, -3&12, 3&-12, and so on.
Now, we need to see which of these combinations, when added, will equal -9 (since the second term of our trinomial is -9x).
The only combination that could equal -9 when added is -12 and 3.
So:
x^2 - 9x - 36 = 0
(x-12)(x+3)= 0
So for this to equal zero, x = 12 or x = -3.
Your answers are x = 12 and x = -3.
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