SSC CHSL Model Paper 17

Question : 62 of 100

Marks: +1, -0

If a + b + c = 6 and ab + bc + ca = 4, then

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

is equal to :

Solution:

a + b + c = 6

(a + b + c)^2 = 62

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

2(ab + bc + ca) = 36

a^2 + b^2 + c^2 + 2 × 4 = 36

a^2 + b^2 + c^2 =36-8 = 28

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

= (a + b + c)

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

= 6[28 - 4] = 6 × 24 = 144

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