prove that sin70.sin50.sin30.sin10=1/16
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1/4 (2sin70.sin50)(2sin30.sin10)
=> 1/4{cos20-cos120}{cos20-cos40}
=> 1/4 {cos^220-cos20.cos40+1/2cos20-1/2cos40}
=> 1/8 (1+cos40)-1/8(cos60+cos20)+1/8cos20-1/8cos40
=> 1/8-1/16=1/16
=> 1/4{cos20-cos120}{cos20-cos40}
=> 1/4 {cos^220-cos20.cos40+1/2cos20-1/2cos40}
=> 1/8 (1+cos40)-1/8(cos60+cos20)+1/8cos20-1/8cos40
=> 1/8-1/16=1/16
abhi178:
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this can be solved by using identities
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