SSC CGL Model Paper 20

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Question : 62 of 100

Marks: +1, -0

If

a^3 + b^3 = 19

and a + b = 1, then what is the value of ab ?

5
-6
7
-9

Solution:

a^3 + b^3 = 19

and a + b = 1
∵

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

⇒

19 = ( 1)^3 - 3 × ab × (1)

⇒

19 = 1 -3ab

⇒

3ab = -18

∴

ab =-18/3=-6

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