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Algebra Level 5

SOLVE IT

A C D B

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3 solutions

Karthik Sharma
Nov 14, 2014

1 1 + 2 1947 + 1 2 1947 + 2 1947 \frac { 1 }{ 1+{ 2 }^{ \sqrt { 1947 } } } +\frac { 1 }{ { 2 }^{ 1947 }+{ 2 }^{ \sqrt { 1947 } } }

= 1 1 + 2 1947 + 1 1 + 2 1947 ( 1 2 1947 ) =\frac { 1 }{ 1+{ 2 }^{ \sqrt { 1947 } } } +\frac { 1 }{ 1+{ 2 }^{ \sqrt { 1947 } } } \left( \frac { 1 }{ { 2 }^{ \sqrt { 1947 } } } \right)

= ( 1 + 1 2 1947 ) ( 1 1 + 2 1947 ) =\left( 1+\frac { 1 }{ { 2 }^{ \sqrt { 1947 } } } \right) \left( \frac { 1 }{ 1+{ 2 }^{ \sqrt { 1947 } } } \right)

= ( 2 1947 + 1 2 1947 ) ( 1 1 + 2 1947 ) =\left( \frac { { 2 }^{ \sqrt { 1947 } }+1 }{ { 2 }^{ \sqrt { 1947 } } } \right) \left( \frac { 1 }{ 1+{ 2 }^{ \sqrt { 1947 } } } \right)

= 1 2 1947 =\frac { 1 }{ { 2 }^{ \sqrt { 1947 } } }

Similarly pairing remaining terms (Note that there is no term without a pair), we get,

n = 0 1947 1 2 n + 2 1947 \sum _{ n=0 }^{ 1947 }{ \frac { 1 }{ { 2 }^{ n }+\sqrt { { 2 }^{ 1947 } } } }

= 974 2 1947 \frac { 974 }{ { 2 }^{ \sqrt { 1947 } } }

This is what I did in the exam but didn't mark the option as there was no option matching to the above answer. And I got home and realised what a fool I was, FORGOT to cancel common factor 2. AGHHH!!!!!!!!

So, the answer is

= 487 2 1945 \boxed{\frac {487 }{ { 2 }^{ \sqrt { 1945 } } }}

Need help in LaTeX to make text bigger.

I used this method only .I love partial fractions.

Rajarshi Chatterjee - 6 years, 7 months ago

this is the second question of part 2 of SA stream KVPY exam 2014 and i solved it correctly.

Yes you are correct this question appeared in KVPY!!

Parth Lohomi - 6 years, 6 months ago
Mehul Chaturvedi
Nov 13, 2014

Just add the first-last term,second-second last and so on U WOULD OBSERVE A MAGIC Can anyone guess

Yeah!! Previous KVPY.

Satvik Golechha - 6 years, 7 months ago

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Would you upload solution?

Mehul Chaturvedi - 6 years, 7 months ago

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Can't. I didn't solve the problem, you know.

Satvik Golechha - 6 years, 7 months ago

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