For the differential equation in given question find a particular solution satisfying the given condition.
dydx=ytanx, y=1 when x=0
Given,dydx=ytanx
On separating the variables, we get 1ydy=tanxdx
On integrating both sides, we get
∫1dy=∫tanxdx⇒log|y|=log|secx|+log|C|⇒logy=log|Csecx| [∵logm+logn=logmn]⇒y=Csecx (∵logm=logn⇒m=n)....(i)
Now, put y=1 when x=0, we get
1=Csec0⇒1=C×1⇒C=1
On substituting C=1 in Eq.(i), we get y=secx
which is the required particular solution.