Trig identities and equations · Year 11
In Year 11 you learn: trig identities.
Trig identities are equations that are true for every angle. The two key ones let you rewrite expressions and solve trig equations, which usually have more than one solution in a given range.
Key facts
- sin²θ + cos²θ = 1.
- tan θ = sin θ ÷ cos θ.
- sin is positive in the 1st and 2nd quadrants; cos in the 1st and 4th; tan in the 1st and 3rd.
- Solutions of sin θ = k: θ and 180° − θ; of cos θ = k: θ and 360° − θ; of tan θ = k: θ and θ + 180°.