SSC CGL Model Paper 19

Question : 70 of 100

Marks: +1, -0

If a + b + c = 13 and ab + bc + ca = 54, then

a^3 + b^3 +c^3 - 3abc

is equal to

Solution:

a^3 + b^3 + c^3 - 3abc

= (a + b + c)

(a^2 + b ^2 + c^2 - ab- be - ca)

(a + b + c)^2

= a ^2 + b^2 + c^2

+ 2ab + 2bc + 2ca

169 - 108 = a^2 + b^2 + c^2

a^2 + b^2 + c^2 = 61

a^3 + b^3 + c^3 - 3abc

= (13) (61 - 54) = 91

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