If = 3, then find the value of
- AOption (a)
324
- BOption (b)
323
- COption (c)
322
- DOption (d)
321
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Correct answer
322
Why this answer is correct
Shortcut Trick
Given: a + 1/a = 3
Shortcut: Use the identity: a6 + 1/a6 = (a2 + 1/a2)3 − 3(a2 + 1/a2).
First, a2 + 1/a2 = (a + 1/a)2 − 2 = 32 − 2 = 7.
Now, a6 + 1/a6 = 73 − 3(7) = 343 − 21 = 322.
∴ Answer = 322
Alternate Method
Given:
a + 1/a = 3
Formula used:
a6 + 1/a6 = (a2 + 1/a2)3 − 3(a2 + 1/a2)
Calculations:
Step 1: a2 + 1/a2 = (a + 1/a)2 − 2
⇒ a2 + 1/a2 = 32 − 2 = 9 − 2 = 7
Step 2: a6 + 1/a6 = (a2 + 1/a2)3 − 3(a2 + 1/a2)
⇒ a6 + 1/a6 = 73 − 3(7) = 343 − 21 = 322
∴ The correct answer is 322.
Additional Information
Formula for Higher Powers
For any n, an + 1/an can be derived using lower powers and substitution.
Key Identity Used
a6 + 1/a6 = (a2 + 1/a2)3 − 3(a2 + 1/a2).
Shortcut for a2 + 1/a2
a2 + 1/a2 = (a + 1/a)2 − 2 — useful for intermediate steps.