SSC CGL Model Paper 8

Question : 62 of 100

Marks: +1, -0

If a - b = 2 and ab = 8, then what is the value of

a^3 - b^ 3\ ?

Solution:

a - b = 2 and ab = 8
∴

(a - b)^2 = (2)^2

⇒

a^2 + b^2 - 2 a b = 4

⇒

a^2 + b^2- 2×8 = 4

⇒

a^2 + b^2 =4 + 16 =20

∴

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

= 2 × (20 + 8)

= 2 × 2 8 = 56

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