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Can somebody help me in understanding how the answer will be C for this.
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- jayhawk2001
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a^4 - b^4 = (a^2 + b^2) * (a^2 - b^2)
1 - insufficient. We don't know a^2+b^2
2 - insufficient. Again, we don't know a^2+b^2
1 and 2 together gives you
a^2 - b^2 = 16
(a+b)*(a-b) = 16
8*(a-b) = 16
a-b = 2, a+b = 8. We can solve for a and b and hence we can get
a^4 - b^4
So, C
1 - insufficient. We don't know a^2+b^2
2 - insufficient. Again, we don't know a^2+b^2
1 and 2 together gives you
a^2 - b^2 = 16
(a+b)*(a-b) = 16
8*(a-b) = 16
a-b = 2, a+b = 8. We can solve for a and b and hence we can get
a^4 - b^4
So, C
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a^4 - b^4 = (a^2-b^2) (a^2+b^2)
Statement I : We know one part, but we don't know (a^2+b^2)
hence insufficient
Statement II : (a-b)=8
Clearly insufficient
Combining I and II :
We know a^2 - b^2 = 16
or (a+b) (a-b) = 16
or (a+b) * 8 = 16
or a+b = 2
Hence we know a+b = 2
and a-b = 8
SO solve simultaneously to get values for a and b....
Statement I : We know one part, but we don't know (a^2+b^2)
hence insufficient
Statement II : (a-b)=8
Clearly insufficient
Combining I and II :
We know a^2 - b^2 = 16
or (a+b) (a-b) = 16
or (a+b) * 8 = 16
or a+b = 2
Hence we know a+b = 2
and a-b = 8
SO solve simultaneously to get values for a and b....