Introduction To Trigonometry

For an acute angle θ

For an acute angle θ in a right triangle: sin θ = opposite/hypotenuse, cos θ = adjacent/hypotenuse, tan θ = opposite/adjacent, cosec θ = hypotenuse/op

sin θ and cosec θ

sin θ and cosec θ are reciprocals (sin θ × cosec θ = 1), cos θ and sec θ are reciprocals (cos θ × sec θ = 1), tan θ and cot θ are reciprocals (tan θ ×

Three basic identities

Three basic identities: (1) sin²θ + cos²θ = 1, (2) sec²θ - tan²θ = 1, (3) cosec²θ - cot²θ = 1. These are derived from Pythagoras theorem and remain tr

If A + B = 90°

If A + B = 90°, then sin A = cos B, cos A = sin B, tan A = cot B, cot A = tan B, sec A = cosec B, cosec A = sec B. This means sin(90° - θ) = cos θ, co

Method 1

Method 1: When two sides given, use Pythagoras theorem to find third side, then calculate ratios. Method 2: When one ratio given, assume proportional