Given the polar equation:

r= theta + sin(3theta), theta is greater than or equal to 0 and less than or equal to pi,

Determine the angle which corresponds with the x-coordinate, 3.

OK, so I tried to solve this using the formula such as r^2= x^2 +y^2 ,x=rcos(theta), y=rsin(theta), tan(theta)=y/x ,but I ended up with a really long equation.

Sorry that everything is written out. I don't know how to write the equations using the actual notation.

Help, please?