Solve the differential equation dydx − 3y cotx = sin2x, y = 2 when x =π2 .
dydx + (-3 cot x)y = sin 2x
It is an L.D.E in y
P = -3 cot x, Q = sin 2x
I.F = e∫pdx = e−3logsinx=1sin3x
G.S: y (IF) = ∫Q (IF) dx + c
ysin3x = ∫ 2sinx cosxsin3x dx + c
y cosec3x = 2 (−1sinx)+c .....(1)
(1) passes through (π2,2)
⇒ 2 = - 2 + c ⇒ c = 4
⇒ y cosec3 x = −2sinx + 4