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Re: SL math questions (URGENT!)


justforlaugh

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HEY,PLEASE HELP (:

(1+ax)^n=1-12x+63x^2-....

Find out the values of a and n.

These are the 2 binomial equation i obtained before i got stuck.

nC2(a)^2=63 and n(ax)=-12

"n(ax)=-12" This isn't right--you already canceled the x on the right side, but you didn't on the left side. So what you're left with is

n(a)=-12

nC2(a2)=63 --> n!/[(n-2)!2] * a2 = 63 --> n(n-1)(a2) / 2 = 63 --> n(n-1)(a2) = 126

**Edit: If you didn't get how to simplify the factorial, think of n as any number. For example, 12. so 12!/(12-2)! = 12*11*10!/(12-2)! = 12*11*10!/10! = 12*11. **

Now it's a system of equations... just gotta substitute and solve.

n(a)=-12 so a= -12/n

Now plug into the second equation

n(n-1)(144/n2)=126 Simplify

(n-1)(144/n)=126

(n-1)(144)=126n

144n - 144=126n

18n - 144=0

18n=144

n=8

Now for a.

a=-12/n so a=-12/8 = -3/2

If this is an MC question, plug in values. If not, guess some numbers if you have no clue.

Edited by sweetnsimple786
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