You will also find that there are terms of the following from, you will also find that there will be 4 times summation n equal to 1 through N naught, you will get sin square beta n. Basically, this term plus 2 times sin square alpha and this term, ok.
फिर आप कुछ टर्म्स ऐसे भी पाएंगे जो निम्नानुसार है, तो एक्सप्रेशन बन जायेगा