Find all the points of a cycloid described by xat sin t and

Find all the points of a cycloid described by x=a(t - sin t) and y= a(1-cos t) where the tangent line is horizontal and a not equal 0 is a constant.

slope of the tangent = dy/dx = (dy/dt)/(dx/dt) = asint/a(1-cost) = cos(t/2) the points where tangent line is horizontal is slope = 0 ==> cos(t/2) = 0 ==> t=(2n+1)pi where not zero is t not equal to (2n+1)pi