Question

if a-b=7 a^2+b^2=85 find a^3-b^3

Answer 1

(a-b)^2=a^2+b^2-2ab
49=85-2ab
2ab=36
ab=18

a^3-b^3
(a-b)(a^2+b^2+ab)
7×(85+18)
7×103
721 Ans

Answer 2

Answer:

a-b = 7

(a-b)² = 7²

a²+b² - 2ab = 49

(a²+b²) -2ab = 49

85 -2ab = 49

2ab = 36

ab = 18

Now,

a³-b³ = (a-b)³+3ab (a-b)

        = (7)³ + 3 x 18 x 7

        = 343 + 378

        = 721