Calculate point

I am wanting to create a 3d line. I need to calculate the destination point as I have the source point.

The y coordinate of the line is both the same for the source and destination coordinate. Because of this, am I correct in saying I can just calculate using 2d maths with trig?

I have the angle and the length of the line.

I have tried this, yet it doesn't work:

x = start_x + len * cos(angle);
z = start_z + len * sin(angle);

thanks

Canning