1.

`int_(0)^(pi)(x tanx)/(sec x +tan x)dx`

Answer» माना `I=int_(0)^(pi)(x tan x)/(sec x+ tanx)dx" …(1)"`
`rArr" "I=int_(0)^(pi)((pi-x)tan(pi-x))/(sec(pi-x)+tan(pi-x))dx`
`" "` [ प्रगुण (4 ) से ]
`=int_(0)^(pi)(-(pi-x)tanx)/(-secx-tanx)dx`
`rArr" "I=int_(0)^(pi)((pi-x)tanx)/(secx+tanx)dx" ...(2)"`
समीकरण (1 ) और (2 ) को जोड़ने पर
`2I=int_(0)^(pi)(x tanx +(pi-x)tanx)/(secx+tanx)dx`
`=int_(0)^(pi)(pi tan x)/(secx+tanx)dx`
`=pi int_(0)^(pi)(tanx(secx - tanx))/(sec^(2)x-tan^(2)x)dx`
`=piint_(0)^(pi)(tanxsecx-tan^(2)x)dx`
`=pi int_(0)^(pi)(tanx sec x - sec^(2)x+1)dx`
`=pi[secx - tanx+x]_(0)^(pi)`
`=pi[(secpi-tanpi+pi)-(sec 0 - tan0+0)]`
`=pi[-1-0+pi-1-0+0]`
`=pi(pi-2)`
`rArr" "I=pi((pi)/(2)-1)`


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