In a coordinate plane the two axes divide the plane in four equivalent parts called quadrants. If terminal ray of an angle in standard position coincides with any axis, then it is called quadrantal angle. The measure of a quadrantal angle is multiple of 90°. For example; 0°, 90°, 180°, 270°, 360°, 450°, … are quadrantal angles. In radian measure quadrantal angle is a multiple of π/2. For example; 0, π/2, π, 3π/2, 2π, 5π/2, 3π, … are quadrantal angles.
Trigonometric Ratios
The ratio between any two sides of a right-angled triangle is called trigonometric ratio.
In triangle ABC, ∠C = 90° and ∠A = 0.
With respect to acute angle θ, BC = a is length of perpendicular, AC = b is length of base and AB = c is length of hypotenuse.
Various trigonometric ratios are defined as: