Simple but important

Evaluate:

0∫πxtanx dx/(secx + tanx)

7 Answers

62
Lokesh Verma ·

0∫πxtanx dx/(secx + tanx) dx

=
0∫π x sinx dx/(1 + sinx) dx

=0∫π (π-x) sin(π-x) dx/(1 + sin(π-x)) dx

=0∫π (π-x) sinx dx/(1 + sinx) dx

taking the sum,

2I=0∫π πdx

2I=Ï€2

I=Ï€2/2

Check if there are mistakes :)

11
Anirudh Narayanan ·

Bhaiya, i think there are mistakes :(

Not so important mistake:

There are two dx in each step :P

Very important mistake:

While adding, remaining term will not be π but π sinx/(1+ sinx) :( (PLs correct me if i'm wrong)

11
Anirudh Narayanan ·

Bhaiya, even though u have taken the sum wrongly, the final answer is correct! [11]
How? [5][5][5][5][5]

11
Anirudh Narayanan ·

Some one care to reply [2]

1
Philip Calvert ·

kya reply kare??

u are right bhaiyya did a mistake there

11
Anirudh Narayanan ·

Arey but how is the final answer correct? [5][5][5][5][5][5]

11
Anirudh Narayanan ·

Here is the actual method:

Steps are same as bhaiya has done till that addition part

2I = π0∫πsinx dx/(sinx+1)

Multiply and divide by 1-sinx

2I = π0∫π(sinx-sin2x) dx/cos2x

= π[ 0∫π(sinx dx/cos2x - 0∫πsec2x-1 dx ]

on evaluating, we get

I = π2/2

The answer which Nishant bhaiya got by doing the sum wrongly [5]

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