Question
If cos 39° = x/ â(x2 + y2),Â
 then the value of tan 51° = ?Solution
cos 39° = x/ â(x 2 + y 2) =  Base/hypotenuse So base = x & hypotenuse = 
so perpendicular = y But for angle 51° which is complimentary of 39° , perpendicular =y & base = x. So tan 51° = base/perpendicular = Alternate Method : cos 39° = OR sin (90°-39°) = OR sin 51° =   -----(1) Squaring on both sides, we will get, sin2 51° = or 1 - cos2 51° = or cos2 51° = 1 - = So cos 51° =  ----(2) Hence tan 51° = sin51°/ cos51° =
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