Hence 1 + tan2 θ = sec2 θ (3) Dividing each term of equation (1) by b2 gives:
b2 + b
b2 = c
)2 + 1 = ( c
Hence cot2 θ + 1 = cosec2 θ (4) Equations (2), (3) and (4) are three further examples of trigonometric identities. For the proof of further trigonometric identities, see Section 16.2.