Can anyone help me out with this question? It's really the third part that I'm having trouble with, but I'll type out the whole thing here. It asks;

In the figure, ABCD is a rhombus in which AB = 60cm and angle A = 60 degrees. P is a point on AD and AP = AQ = 2cm. Angle PQC = x degrees. P is joined to C.

a) Write down the length of PQ, giving reasons.

b) Show that PC = QC

c) Yse the cosine rule for the triangle QBC and, using part b), show that .