Here's my problem. I have a rotating wheel, radius 40cm, and a connecting rod AP with length 1.2m. The pin P slides back and forth along the x-axis as the wheel rotates counterclockwise at a rate of 360 revolutions per minute. Find the angular velocity of the connecting rod, , in radians per second, when .

I have attached a diagram, and my work on the problem so far. (NOTE: later in my work, for the sake of simplicity, i replaced with "a" and with "O".)

Now, this is my problem. At the bottom, where i differentiated it, the derivative doesnt have an alpha in the equation, but i need it in the problem to solve it. I had to use the calculator to differentiate it, because i havent worked with differentiating before. I just became completely lost at this point...am i going about the problem the wrong way?....................(The first picture is the top half, the second is the bottom half)