dxdy+2ytanx=sinx
I.F.=e∫2tanxdx=e2lnsecx
I.F.=sec2x
y.(sec2x)=∫sinx.sec2xdx+C
y.(sec2x)=∫secxtanxdx+C
y.(sec2x)=secx+C
x=3π;y=0
⇒C=−2
⇒y=sec2xsecx−2=cosx−2cos2x
Let cosx=t,−1≤t≤1
⇒y=t−2t2⇒dtdy=1−4t=0⇒t=41
Second-order derivative is negative
∴max=41−81=82−1=81