Basic Trigonometric Identities

Trigonometric Identities are

1. cos ²  θ + sin ²  θ = 1
2. 1 + tan ²  θ = sec ²  θ
3. 1 + cot ²  θ = cosec ²  θ

How do we remember them?

We should only remember

cos ²  θ + sin ²  θ = 1

For other identities,

just divide by sin ²  θ or cos ²  θ  

cos ²  θ + sin ²  θ = 1

Divide by  cos ²  θ  

cos ²  θ/cos ²  θ + sin ²  θ/cos ²  θ = 1/cos ²  θ

1 + tan ²  θ = sec ²  θ

cos ²  θ + sin ²  θ = 1

Divide by  sin ²  θ  

cos ²  θ/sin ²  θ + sin ²  θ/sin ²  θ = 1/cosec ²  θ

cot ²  θ + 1 = cosec ²  θ