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Grade: 11
        
I did not understand how to solve these three questions.....................
11 months ago

Answers : (2)

Aditya Gupta
1673 Points
							
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)

11 months ago
Aditya Gupta
1673 Points
							
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
11 months ago
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