Pythagorean Identites

  • sin2 θ + cos2 θ = 1.
  • tan2 θ + 1 = sec2 θ
  • 1 + cot2 θ = sec2 θ
  • tan^2= sec^2 -1
  • sec= 1/cos
  • cot= 1/tan
  • csc= 1/sin
  • tan = sin/cos
  • cot = cos/sin
  • Odd: sin (- beta) = -sin/ csc (- beta) = -csc, tan (-beta) = -tan
  • Even: cos (-beta) = cos, sec (- beta) = sec
  • 1 = cot^2 - csc^2
  • cot^2 = 1- csc^2
  • sin^2 = 1 - cos^2
  • cos^2 = 1 - sin^2