oh! i wasnt trying to differentiate that equation

it started out as r=2+2cos(theta)

then i did y=rsin(theta)

dy/d(theta)=2cos(theta) + 2 cos^2(theta) - 2sin^2(theta) simplified down to

4cos^2(theta) + 2cos(theta) -2

so dy/dx = slope. i have to replace the thetas in 4cos^2(theta) + 2cos(theta) -2 with pi/2. but i dont know how to calculate 4cos^2(theta)......