Let y = y(x) be the solution of the differential equation

dydx+2y2cos4xcos2x=xetan1(2cot2x), 0<x<π2withy(π4)=π232.

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1 Answer
A
8 months ago

2cos4 x – cos2x = 2(1+cos2x2)2cos2x

=1+cos22x2

22dx1+cos22x=22sec22xdx2+tan22x

=212tan1(tanx2)

now IF = ePdx

e22sec22xdx2+tan22x=etan1(tan2x2)

Solution: yetan1(tan2x2)=x.etan1(2cot2x)etan1(tan2x2)dx

yetan1(tan2x2)=x22eπ/2+C

at x=π4,y=π232,C=0

at x=π3,y=π218etan1α

yetan1(tan2π3)2=π218eπ/2

π218etan1αetan1(32)=π218eπ/2

tan-1 a + tan-1 (3/2)=π2

cot-1a = tan-1 (32)

tan-1 1α=tan1(32)

1α=3/2

2 = 23

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