If a^3 + b^3 = 72 and ab = 8, then what is the value of a + b?

SSC CGL Model Paper 6

Question : 62 of 100

Marks: +1, -0

a^3 + b^3 = 72

and ab = 8, then what is the value of a + b?

Solution:

a^3 + b^3 = 72,ab = 8

Let

a+b=x

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

x ^3 = 72 + 3 ×8x

x^ 3-2 4 x = 72

x (x ^2-24) = 6 ×12

x = 6
∴

a + b = 6

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