SSC CGL 12 Jun 2019 Shift 1 Paper

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Question : 67 of 100

Marks: +1, -0

If

a+b+c=6

and

a b+b c+c a=5,

then

a^{3}+b^{3}+c^{3}-

3 a b c

is equal to:

116
126
98
108

Solution:

Let

C=0

a+b=6

ab

=5

Find

a^{3}+b^{3}=?

a+b=6

a^{2}+b^{2}+2 \× 5=36

a^{2}+b^{2}=26

find

=a^{3}+b^{3}

=(a+b)\ (a^{2}+b^{2}-a b\ )

=6(26-5)=6 \× 21=126

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