If a+\frac{1}{a}=5, then a^{3}+{1}/{a^{3}}=?

RRB Group D 3-Oct-2018 Shift 3 Solved Paper

Question : 49 of 100

Marks: +1, -0

a+{1}/{a}=5,

then

a^{3}+{1}/{a^{3}}=?

Solution:

a+{1}/{a}=5,

a^{3}+{1}/{a^{3}}

= (a+1/a)(a^2+1/a^2-1)

=(a+1/a)((a+1/a)^2-3)

=5(5^2-3)=110

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