Question

reduction of order find second solution y2

y”+9y=0 y1=sIn3x

Answer 1

@Wislar

Answer 2

I believe what they want you to do is something of the form:
\[y_1=\sin(3x)\]
where y_1 denotes a solution, then by the principle of superposition:
\[y=c \sin(3x)\] will also be a solution. Now to perform reduction of order, let c be a rather a function of x than a constant, such that:
\[y_2=c(x) \sin(3x)\]