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## Answers

substitute A = 10

cos 10.cos(60+10).cos(60-10)=1/4 cos 3(10)

cos10. cos 70. cos 50 = 1/4 cos 30

multiply cos 30 on both sides

cos 10. cos 30. cos 50. cos 70 = 1/4 cos² 30

= 1/4(√3/2)²

= 1/4(3/4)

=3/16

hence solved