Question

e 10. Prove that : cos 6º cos 42° cos 66° cos 78°
1
16​

Answer 1

Answer:

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Answer 2

Answer:

In this question

cos6×cos42×cos66×cos78 = 1/16

Let, R.H.S

cos6×cos42×cos66×cos78

Multiple and divided by 2

1/2×(2cos42×cos78)×cos6×cos66

1/2×(cos120+cos36)×cos6×cos66

1/2 ×(−sin30 +cos36)×cos6×cos66

1/2×-1/2+√5+1/4 )×cos6×cos66

Again multiple and divided by 2

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