Question

if a+b=12 and ab=27,find the value of a^3+b^3

Answer 1

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Answer 2

a+b=12 ab=27 a^3+b^3=

a+b=12

a=12-b---------------- ( 1 )

ab=27

b=27/a --------------- ( 2 )

a^3+b^3 = (12-b)^3 + (27/a)^3

= 12^3 - b^3 - 3* 12 b ( 12 - b )

=144 - b^3 - 36 b (12-b)

144 - b^3 - 432 b - b^2

-b^3 -b^2 -432 b +144

-b-432 b + 144

- 431 b + 144

144 = 431 b

b= 144 / 431

b = 2.99

a + 2.99 =12

a= 12-2.99

a=  9.01

. ' . a^3 + b^3 = 2901