Trigonometric Identities are
- cos ^{ 2 } θ + sin ^{ 2 } θ = 1
- 1 + tan ^{ 2 } θ = sec ^{ 2 } θ
- 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