SSC CGL 6 Aug 2017 Shift 1 Paper

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Question : 62 of 100

Marks: +1, -0

If

a^3 + b^3 =35

and ab =6, then what is the value of a + b ?

5
8
2
-8

Solution:

a^3 + b^3 =35, ab =6

Let a + b = x

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

⇒

x^ 3 =35+ 3×6x

⇒

x^ 3 -1 8 x = 35

⇒

x ( x^ 2 -18) = 5 × 7

∴

x=5

∴

a+b=5

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