Question

a-b = 7  a²+b²=85 find a³-b³

Answer 1

a - b = 7
a²+b²= 85
using a-b = 7 squaring both sides
a²+b²-2ab = 49
85 - 2ab = 49
ab = 18

so a³-b³ = (a-b)(a² + b² + ab)
            = 7 . (85 + 18)
            = 721 ANSWER

Answer 2

a-b = 7 ; a²+b² = 85

(a-b)²= (7)² ---- squaring both side

a²+b²-2ab = 49

85-2ab = 49

-2ab = 49-85

-2ab = -36

ab = -36/-2

ab= 18

so,

a³+b³ = (a-b) ( a²+ab+b² )

a³+b³ = 7 (85+18)

a³+b³ = 7 (103)

a³+b³ = 721

thank you guys ❤️