What is the value of a^4 - b^4 ?
I a^2 - b^2 = 16
II a + b = 8
Looks obvious at the first look but....
The question can be simplified a^4 - b^4 = (a^2)^2 - (b^2)^2 = (a^2 - b^2) ( a^2 + b^2)
From statement 1(a^2 - b^2) ( a^2 + b^2)
we know the info in blue but can't solve the other part
Statement 2 clearly insufficient
(a+b) (a-b) = 16
and we know a+b = 8
test some numbers (1,7)(2,6),(5,3)
It satisfies both equation. Hence sufficient!
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