nope, that's not the right value for sin(u). there are several ways you can get to sin(u). Two conventional ways are:

Use the fact that

Solve for . Note that we are in the second quadrant so you will need to take the positive square root. As sine is positive in that quadrant.

Another way: Draw a right-triangle with an acute angle . The adjacent side to should be labeled while the hypotenuse should be labeled . Use Pythagoras' Theorem to find the opposite side and use sine = opposite/hypotenuse