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Question: Answered & Verified by Expert
Let y=yx be the solution of the differential equation x tanyxdy=y tanyx-xdx-1x1,y12=π6. Then the area of the region bounded by the curves x=0,x=12 and y=yx in the upper half plane is:
MathematicsDifferential EquationsJEE Main
Options:
  • A 18π-1
  • B

    112π-3

  • C 14π-2
  • D 16π-1
Solution:
2216 Upvotes Verified Answer
The correct answer is: 18π-1
We have,

dydx=xyx·tanyx-1xtanyx
dydx=yx-cotyx

Put y=vx

dydx=v+xdvdx

Now, we get

v+xdvdx=v-cotv

tanvdv=-dxx

lnsecv=-lnx+c

lnsecyx=-lnx+c

lnsecyx+lnx=c

Now, y12=π6, then

lnsecπ3+ln12=c

ln2+ln12=c

ln2-ln2=c

c=0

Hence,

 secyx=1x

cosyx=x

y=xcos-1x

So, required bounded area

=012cos-1xIxIIdx

=cos-1x·x22012+12012x21-x2dx

=π16-120121-x2-11-x2dx

=π16-120121-x2-11-x2dx

=π16-12x21-x2+12sin-1x-sin-1x012

=π16-12x21-x2-12sin-1x012

=π16-1214-π8

=π-18 sq. units

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