SOLUTION: I need help to factor this trinomial -x^2+7x+18 please explain step by step so I can do it myself :)

Question 871368: I need help to factor this trinomial -x^2+7x+18 please explain step by step so I can do it myself :)
Found 2 solutions by rothauserc, mananth:
Answer by rothauserc(4718) (Show Source): You can put this solution on YOUR website!
start by finding the prime factors of 18 which are 3*3*2
we want to factor -x^2 + 7x + 18
we have (-x + ) times (x + )
looking at the prime factors, we want to get a 7, note that 9 times 2 results in the 7, therefore
-x^2 + 7x + 18 = (-x + 9) times (x + 2)

Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!

Multiply the first term and the third term
-18x^2
Split the middle term into two parts such that when you add the parts you get 7x and when you multiply them you get -18x^2
In this case the break up is 9 and- 2
9x-2x=7x
9x*-2x = -18x^2
Re write the trinomial

factorize
-x(x-9)-2(x-9)
(x-9)(-x-2)

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