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by dtweah » Sun Mar 07, 2010 1:05 pm
If a + b = 2 and a^2 + b^2 = 5, then what is the value of a^3 + b^3 ?
(a) 11
(b) 12
(c) 13
(d) 14
(e) 15
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by firdaus117 » Sun Mar 07, 2010 9:33 pm
(a+b)^2=a^2+b^2+2ab
4=5+2ab
ab=-0.5
a^3 + b^3=(a+ b)(a^2+b^2-ab)
= 4(5+0.5)
=22
I am getting 22 as answer.
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by ajith » Sun Mar 07, 2010 11:30 pm
dtweah wrote:If a + b = 2 and a^2 + b^2 = 5, then what is the value of a^3 + b^3 ?
(a) 11
(b) 12
(c) 13
(d) 14
(e) 15
(a+b)^2 = a^2+b^2+2ab

=> 4 = 5 + 2ab
ab = -0.5

a^3+b^3 = (a+b) (a^2+b^-ab)
= 2(5+0.5)
= 2*5.5
= 11
[spoiler]
A[/spoiler]
Always borrow money from a pessimist, he doesn't expect to be paid back.
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by firdaus117 » Sun Mar 07, 2010 11:51 pm
firdaus117 wrote:(a+b)^2=a^2+b^2+2ab
4=5+2ab
ab=-0.5
a^3 + b^3=(a+ b)(a^2+b^2-ab)
= 4(5+0.5)
=22
I am getting 22 as answer.

:oops: So close yet so far!!!
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by ajith » Mon Mar 08, 2010 12:21 am
firdaus117 wrote: :oops: So close yet so far!!!
I do it all the time!
Always borrow money from a pessimist, he doesn't expect to be paid back.
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