Math, asked by de6epJhadasstefreya, 1 year ago

Evaluate: Tan20Tan40Tan60Tan80 = 3

Answers

Answered by Manjula29
27
tan40.tan20.tan80 = tan60 Taking L.H.S. tan40.tan80.tan20 =(sin40 sin80)sin20/cos40 cos80(cos20) =(2sin40 sin80) sin20 / (2cos40 cos80)cos20 =(cos40- cos120) sin20 / (cos120 + cos40) cos20 =(2cos40 + 1)sin20 / (2cos40 - 1) cos20 =2cos40sin20 + sin20 / 2cos40cos20 - cos20 =sin60 - sin20 + sin20 / cos60 + cos20 - cos20 =sin60/cos60 =tan60 = R.H.S.

Manjula29: Tan3A is equal to tan(60+A)tanAtan(60-A) .
The question is tan20tan40tan60tan80
Now we know tan 60 is equal to under root 3 .
Now tan20tan40tan80 is of tan3A form where A= 20 . Therefore tan20tan40tan80 = tan3*20= tan 60= under root 3
There for tan20tan40tan60tan80= under root 3* under root 3= 3
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