find value of 8ab(a^2+b^2) when (a+b) = ✓11 and (a-b) =✓7.
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Answer:
use the identity of (a²-b²)
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(a+b)²-(a-b)²=(√11)²-(√7)²
[(a+b)+(a-b)][(a+b)-(a-b)]=(11-7) ...[by identity (a²-b²)]
(a+b+a-b)(a+b-a+b)=4
(2a)(2b)=4
4ab=4
ab=4
Now,
8ab(a²+b²)
=4ab(2a²+2b²)
=4×4(2a²+2b²+2ab-2ab)
=16[(a²+b²+2ab)+(a²+b²-2ab)]
=16[(a+b)²+(a-b)²]
=16[(√11)²+(√7)²]
=16(11+7)
=16×18
=304
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