prove that : sin20 sin40 sin60 sin80 = 3/16
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sin20sin40sin60sin80
=(cos40−cos80)/2 ×sin40sin80
=cos40sin40sin80−cos80sin40sin80/2
=sin²80−sin40 sin160/ 4
=1−cos160−cos120+cos200/8
=1+cos20−cos120−cos208
=1−cos120/8
=2sin²60/8=3/16 ( hence it proved)
=(cos40−cos80)/2 ×sin40sin80
=cos40sin40sin80−cos80sin40sin80/2
=sin²80−sin40 sin160/ 4
=1−cos160−cos120+cos200/8
=1+cos20−cos120−cos208
=1−cos120/8
=2sin²60/8=3/16 ( hence it proved)
CUTEBARBIE:
plz mark brainlest
can u pls solve it by different method ???
or any other method is available for this or not ??
i think this method is good
but how will it be striked in mind that u have to write cos40-cos80 ?
r u solving it by any other method ???
no,sorry ,i can't
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