Question

A+b=9 ab=20 find the value of a3-b3

Answer 1

(a+b)=9,ab=20

Now,

(a-b)^2 = (a+b)^2 - 4ab

.:(a-b)^2 = (9)^2 - 4×(20)

.:(a-b)^2 = 81 - 80

.:(a-b)^2 = 1

.:(a-b) = 1 ........( by taking square root )

Now,

a^3-b^3 = (a-b)^3 + 3ab(a-b)

.:a^3-b^3 = (1)^3 + 3×20×(1)

.:a^3-b^3 = 1 + 60

.:a^3-b^3 = 61.

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