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Question : What is the value of $\left(k-\frac{1}{k}\right)\left(k^2+\frac{1}{k^2}\right)\left(k^4+\frac{1}{k^4}\right)\left(k^8+\frac{1}{k^8}\right)\left(k^{16}+\frac{1}{k^{16}}\right) ?$

Option 1: $k^{64}-\frac{1}{k^{64}}$

Option 2: $\frac{k^{32}-\frac{1}{k^{32}}}{k-\frac{1}{k}}$

Option 3: $k^{32}-\frac{1}{k^{32}}$

Option 4: $\frac{k^{32}-\frac{1}{k^{32}}}{k+\frac{1}{k}}$


Team Careers360 16th Jan, 2024
Answer (1)
Team Careers360 20th Jan, 2024

Correct Answer: $\frac{k^{32}-\frac{1}{k^{32}}}{k+\frac{1}{k}}$


Solution : Consider, $\left(k-\frac{1}{k}\right)\left(k^2+\frac{1}{k^2}\right)\left(k^4+\frac{1}{k^4}\right)\left(k^8+\frac{1}{k^8}\right)\left(k^{16}+\frac{1}{k^{16}}\right)$
Multiplying and dividing by $(k+\frac{1}{k})$
⇒ $\left(k-\frac{1}{k}\right)\left(k^2+\frac{1}{k^2}\right)\left(k^4+\frac{1}{k^4}\right)\left(k^8+\frac{1}{k^8}\right)\left(k^{16}+\frac{1}{k^{16}}\right)=\frac{(k-\frac{1}{k})(k+\frac{1}{k})(k^2+\frac{1}{k^2})(k^4+\frac{1}{k^4})(k^8+\frac{1}{k^8})(k^{16}+\frac{1}{k^{16}})}{k+\frac{1}{k}}$
Now using, $(a+b)(a-b)=a^2 - b^2$
⇒ $\left(k-\frac{1}{k}\right)\left(k^2+\frac{1}{k^2}\right)\left(k^4+\frac{1}{k^4}\right)\left(k^8+\frac{1}{k^8}\right)\left(k^{16}+\frac{1}{k^{16}}\right)=\frac{(k^2-\frac{1}{k^2})(k^2+\frac{1}{k^2})(k^4+\frac{1}{k^4})(k^8+\frac{1}{k^8})(k^{16}+\frac{1}{k^{16}})}{k+\frac{1}{k}}$
$=\frac{(k^4-\frac{1}{k^4})(k^4+\frac{1}{k^4})(k^8+\frac{1}{k^8})(k^{16}+\frac{1}{k^{16}})}{k+\frac{1}{k}}$
$=\frac{(k^8-\frac{1}{k^8})(k^8+\frac{1}{k^8})(k^{16} + \frac{1}{k^{16}})}{k+\frac{1}{k}}$
$=\frac{(k^{16} - \frac{1}{k^{16}})(k^{16} + \frac{1}{k^{16}})}{k+\frac{1}{k}}$
$=\frac{k^{32} - \frac{1}{k^{32}}}{k+\frac{1}{k}}$
Hence, the correct answer is $\frac{k^{32} - \frac{1}{k^{32}}}{k+\frac{1}{k}}$.

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