SSC CGL Model Paper 10

Question : 62 of 100

Marks: +1, -0

If a + b = 8 and ab = 15, then what is the value of

a^3 + b^3

Solution:

a + b = 8 and ab = 15
∴

(a + b)^2 = (8)^2

⇒

a^2 + b^2 + 2ab =64

⇒

a^2 + b^2 = 6 4 -2 × 1 5

= 6 4 - 3 0 = 34

∴

a^3 + b^3 = (a + b)(a^2 + b^2 - ab)

8 × (3 4 -1 5 ) = 8× 1 9 = 152

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