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JEE Advanced · Mathematics · 27. Definite Integration

Let fx=7tan8x+7tan6x-3tan4x-3tan2x  for all x -π2,π2. Then the correct expression(S) is(are)

  1. A 0π4x fxdx=112
  2. B 0π4 fxdx=0
  3. C 0π4x fxdx=16
  4. D 0π4x fxdx=1
Verified Solution

Answer & Solution

Correct Answer

(B) 0π4 fxdx=0

Step-by-step Solution

Detailed explanation

fx=7tan8x+7tan6x-3tan4x-3tan2x
fx=sec2x7tan6x-3tan2x
Now,
0π4sec2x7tan6x-3tan2x dx
=017t6-3t2dt
=7t77-3t33
=17-13=0
Also
0π4xsec2x 7tan6x-3tan2x dx
tanx=t
01tan-1t7t6-3t2 dt
tan-1tt7-t3|01-0111+t2 t7-t3dt
=-0111+t2 t3t4-1dt
=+01t3 1+t2 1-t2dt1+t2=01t3-t5dt
=14-16=112
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