If a - b = 4 and $a^3 - b^3 = 88 $, then find the value of $a^2 - b^2$.
Answer & explanation
Correct answer: option 4
Given that,
a - b = 4
a3 - b3 = 88
We know that,
(a3 - b3) = (a - b) (a2 + b2 + ab)
(a3 - b3) = (a - b) [(a - b)2 + 3ab]
(a + b)2 = a2 + b2 + 2ab
(a + b)(a - b) = a2 - b2
According to the given data,
88 = 4 × (42 + 3ab)
= 22 = 16 + 3ab
= 3ab = 22 - 16
= ab = 2
(a - b)2 = a2 + b2 - 2ab
= 42 = a2 + b2 - 2 × 2
= a2 + b2 = 16 + 4
= a2 + b2 = 20
(a + b)2 = 20 + 2 × 2
= a + b = √24 = 2√6
Then (a + b)(a - b) = 2√6 × 4 = $8\sqrt{6}$