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I did not understand how to solve these three questions.....................

I did not understand how to solve these three questions.....................

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Grade:11

2 Answers

Aditya Gupta
2081 Points
5 years ago
For the first question note that arguments inside sine are in AP. so use the formula for its summation and you will get zero.

Just use sin α + sin (α + β) + sin (α + 2β) + … to n terms = (sin (nβ/ 2))/ (sin (β/ 2)). sin (α + (n-1)β/2)

Aditya Gupta
2081 Points
5 years ago
For third question, use the identity
sinx*sin(60-x)*sin(60+x)= (sin3x)/4
Put x=6
sin6sin66sin54=sin18/4….(1)
Put x=18
sin18sin42sin78= sin54/4....(2)
Multiply (2) and (1)
sin6sin66sin78sin42= 1/16

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