Question

if a minus b is equal to 7 a square + b square is equal to 85 find a cube minus b cube

Answer 1

Answer:

a^3-b^3=721

Step-by-step explanation:

here,

a-b=7

a^2+b^2=85

so,

[a-b]^2=a^2+b^2-2ab

so 7^2=85-2ab

85-49=2ab

36=2ab

ab=18

hence,

[a-b]^3=a^3-b^3-3ab[a-b]

7^3=a^3-b^3-54*7

343+378=a^3-b^3

a^3-b^3=721

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