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• sec² x + cos² x = 1
• tan x = (sin x) ⁄ (cos x)

Sec, cosec & cot

• sec x = 1 ⁄ cos x
• cosec x = 1 ⁄ sin x
• cot x = 1 ⁄ tan x
  cot x = cos x ⁄ sin x
• sec² x = 1 + tan² x
• cosec² x = 1 + cot² x

Addition formulae

• sin (A+B) = sinAcosB + cosAsinB
• sin (A-B) = sinAcosB - cosAsinB
• cos (A+B) = cosAcosB - sinAsinB
• cos (A-B) = cosAcosB + sinAsinB
• tan (A+B) = tanA + tanB ⁄ 1 - tanAtanB
• tan (A-B) = tanA - tanB ⁄ 1 + tanAtanB

Double angle formulae

• sin2A = 2sinAcosA
• cos2A = cos²A - sin²A
  cos2A = 2cos²A - 1
  cos2A = 1 - 2sin²A
• tan2A = 2tanA ⁄ 1 - tan²A