In a question like: C(n,2)=45

n(n-1)=90

n2-n-90=0

(n-10)(n+9)=0 <- how do you know which to make the positive and which to make the negative?

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- Dec 3rd 2008, 10:19 AMCarrickNeed a little freshened up
In a question like: C(n,2)=45

n(n-1)=90

n2-n-90=0

(n-10)(n+9)=0 <- how do you know which to make the positive and which to make the negative? - Dec 3rd 2008, 10:41 AMbearej50
solve n+9=0 and n-10=0. n=10. 10 is positive. Just solve both after setting both to 0.