Solving Linear Differential Equations of First Order
If y = y x is...
Question
If y=y(x) is the solution of the differential equation dydx+2ytanx=sinx,y(π3)=0 then the maximum value of the function y(x) over R is equal to:
A
−154
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B
12
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C
8
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D
18
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Solution
The correct option is D18 dydx+2tanx.y=sinxI.F.=eln(sec2x)=sec2x⇒ysec2x=∫tanxsecxdx=secx+cNow x=π3,y=0⇒c=−2∴y=cosx−2cos2xy=−2(cos2x−12cosx)=−2((cosx−14)2−116)⇒y=18−2(cosx−14)2∴ymax=18