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Reduction Formulae Application

shamieh

Active member
Sep 13, 2013
539
Can someone show me how I would "use" the reduction formulae for \(\displaystyle tan^n x\) ? I just want to see an example on when I would ever use it. A simple one will do.


\(\displaystyle \frac{tan^{n-2}x}{n - 1} - \int tan^{n-2} x dx\)
 
Last edited:

soroban

Well-known member
Feb 2, 2012
409
Hello, shamieh!

Your formula is incorrect.

[tex]\int\tan^n\!x\,dx \;=\;\frac{\tan^{n-1}\!x}{n - 1} - \int\tan^{n-2}\!x\,dx[/tex]


Example: .[tex]\int\tan^4\!x\,dx[/tex]

Substitute [tex]n=4[/tex] into the formula:

[tex]\int\tan^4\!x\,dx \;=\;\tfrac{1}{3}\tan^3\!x - \int \tan^2\!x\,dx[/tex]

. . . . . . . . . [tex]=\;\tfrac{1}{3}\tan^3\!x - \int(\sec^2\!x -1)\,dx [/tex]

. . . . . . . . . [tex]=\;\tfrac{1}{3}\tan^3\!x - \int\sec^2\!x\,dx + \int dx[/tex]

. . . . . . . . . [tex]=\;\tfrac{1}{3}\tan^3\!x - \tan x + x + C[/tex]
 

shamieh

Active member
Sep 13, 2013
539
Thank you sororaban! Also thank you for the PM the other day!