Database - Trigonometry

• Ahm97sic

  17 Oct 08, 01:37

  Question

  Without using a calculator,

  evaluate tan ( tan-1 2 + tan-1 8)

  (The number in red is in superscript)

  Answer

  tan (tan-1 2 + tan-1 8)

  Let tan-1 2 = x. Hence, tan x = 2

  Let tan-1 8 = y. Hence, tan y = 8

  tan (x + y)

  = [tan x + tany] / [1 - tanx tany]

  = [2 + 8 ] / [1 - (2)(8)]

  = - 2/3

   

• Garrick_3658

  18 Oct 08, 18:59

  I think you forgot:

  Let tan-1 8 = y. Hence, tan y = 8

  Thanks.

• Ahm97sic

  18 Oct 08, 19:59

  Dear Darrick_3658,

  Yes, I have forgotten to type

  Let tan-1 8 = y. Hence, tan y = 8

  Thanks.

  Regards,

  ahm9s7ic