Question

prove that cos20.cos40.cos80=1/8

Answer 1

✔️✔️Firstly in equation 1 use the formula :----

⏹2sinAcosA=Sin2A
and simplify the terms ..

In the second equation use the formula:-----
⏹2sinAcosA=Sin2A


✔️So substituting and further simplifying by taking common terms we get :-

⏹sin(180-20)/8 sin20 where take the formula sin(180-A)=sinA..

and thus cancelling the sin20°terms we get the simplified answer as :--

⏹➖1/8➖⏹

Answer 2

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