trig

• • sec = 1/cos
  • cosec = 1/sin
  • cot = cos/sin = 1/tan
• double angle formulae

  • sin2A = 2sinAcosA
  • cos2A = cos^2(A) - sin^2(A) = 2cos^2(A) - 1 = 1 - 2sin^2(A)
  • tan2A = 2tanA/(1 - tan^2(A))