excos y dx – exsin y dy = 0
⇒ excos y dx = exsin y dy
⇒ x = -log t + c
Resubstitute t
⇒ x = -log(cosy) + c
⇒ x + c = log(cosy)-1
⇒ excos y = e-c
As e is a constant c is the integration constant hence e-c is a constant and hence let it be denoted by k such that k = e-c
⇒ excos y = k