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Grade 11Trigonometry

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

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Profile image of Harnoor
7 Years agoGrade 11
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2 Answers

Profile image of Aditya Gupta
ApprovedApproved Tutor Answer7 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)

Profile image of Aditya Gupta
7 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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