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Question
If `3"x"-1/(3"x")=5`, find : `81"x"^4+1/(81"x"^4)`
Sum
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Solution
`81"x"^4+1/(81"x"^4)=(9"x"^2+1/(9"x"^2))^2-2`
= (27)2 − 2
= 729 − 2
= 727
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Important Formula of Expansion
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