Trigonometry — Important Questions

sin 30° = 1/2, cos 60° = 1/2, cos 30° = √3/2

From standard trigonometric values: sin 30° = 1/2, cos 30° = √3/2, sin 60° = √3/2, cos 60° = 1/2. The incorrect option is sin 60° = 1/2 (it should be √3/2).

3/5

Using the complementary angle identity: sin(90° - θ) = cos θ. Therefore, if sin(90° - θ) = 3/5, then cos θ = 3/5.

sin²θ + cos²θ = 1, sec²θ - tan²θ = 1, cosec²θ - cot²θ = 1

The three fundamental trigonometric identities are: sin²θ + cos²θ = 1, sec²θ - tan²θ = 1, and cosec²θ - cot²θ = 1. The option tan²θ + cot²θ = 1 is incorrect.

1

At 0°, the adjacent side equals the hypotenuse, so cos 0° = adjacent/hypotenuse = 1.