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Evaluate: ∫dxx[(logx)2+4logx-1]

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Question

Evaluate: `int "dx"/("x"[(log "x")^2 + 4 log "x" - 1])`

Sum
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Solution

Let I = `int "dx"/("x"[(log "x")^2 + 4 log "x" - 1])`

Put log x = t

∴ `1/"x" "dx" = "dt"`

∴ I = `int "dt"/("t"^2 + 4"t" - 1)`

`= int 1/("t"^2 + 4"t" + 4 - 4 - 1)`dt

`= int 1/(("t + 2")^2 - 5)` dt

`= int 1/(("t + 2")^2 - (sqrt5)^2)` dt

`= 1/(2 sqrt5) log |("t" + 2 - sqrt5)/("t" + 2 + sqrt5)|` + c

∴ I = `1/(2 sqrt5) log|(log"x" + 2 - sqrt5)/(log "x" + 2 + sqrt5)|` + c

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Chapter 5: Integration - MISCELLANEOUS EXERCISE - 5 [Page 139]

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Balbharati Mathematics and Statistics 1 (Commerce) [English] Standard 12 Maharashtra State Board
Chapter 5 Integration
MISCELLANEOUS EXERCISE - 5 | Q IV. 3) v) | Page 139

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