RRB Group-D Model Paper 13 with answers for online practice

Question : 5 of 100

Marks: +1, -0

If a + 1/a = 5, find the value of

a^2 + 1/a^2

Solution:

GIVEN:
a + 1/a = 5
FORMULA USED:

(a + b)^2 = a^2 + b^2 + 2ab

CALCULATION:
We have,

(a + b)^2 = a^2 + b^2 + 2ab

Substituting 1/a in place of b, we have

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

⇒ 25 =

a^2 + 1/a^2 + 2

⇒

a^2 + 1/a^2

= 25 - 2 = 23.

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