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Question -

Find (x + 1) 6 + (x – 1) 6. Hence,or otherwise evaluate (√2 + 1)6 + (√2 – 1)6.



Answer -

Firstly, let us solvethe given expression:

(x + 1) 6 +(x – 1) 6

The above expressioncan be expressed as,

(x + 1) 6 +(x – 1) 6 = 2 [6C0 x6 + 6C2 x4 + 6C4 x2 + 6C6 x0]

= 2 [x6 +15x4 + 15x2 + 1]

Now,

Let us evaluate theexpression:

(√2 + 1)6 +(√2 – 1)6

So consider, x = √2then we get,

(√2 + 1)6 +(√2 – 1)6 = 2 [x6 + 15x4 + 15x2 +1]

= 2 [(√2)6 +15 (√2)4 + 15 (√2)2 + 1]

= 2 [8 + 15 (4) + 15(2) + 1]

= 2 [8 + 60 + 30 + 1]

= 198

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