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mgmat odd-ball question

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mgmat odd-ball question

by niraj_a » Sat Dec 06, 2008 6:24 am
this question is easy, but i made a simple mistake - used simultaneous equations at the end to cancel off. why did that not work?

If #p# = ap3+ bp – 1 where a and b are constants, and #-7# = 3, what is the value of #7#?

5
0
-2
-3
-5

OA -5
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by stop@800 » Sat Dec 06, 2008 11:03 am
#p# = ap3+ bp – 1

#-7# = 3

hence
a(-7)3+ b(-7) – 1 = 3

-a(7)3 - b(7) – 1 = 3

a(7)3 + b(7) + 1 = -3

a(7)3 + b(7) -1 + 2 = -3

a(7)3 + b(7) -1 = -5

#7# = -5

Hope this helps
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