CLASS-9
TRIGONOMETRICAL RATIOS - T-RATIOS OF AN ANGLE
Trigonometrical Ratios (T-Ratios) of an Angle –
In △ABC, let ∠B = 90⁰ and let ∠A be acute.
For ∠A, we have –
Base = AB, Perpendicular = BC, and Hypotenuse = AC. The T-ratios for ∠A are defined as –
Perpendicular BC
(i) Sine = --------------- = -------, written as sin A
Hypotenuse AC
Base AB
(ii) Cosine A = -------------- = -------, written as cos A
Hypotenuse AC
Perpendicular BC
(iii) Tangent A = ---------------- = -------, written as tan A
Base AB
Hypotenuse AC
(iv) Cosecant A = ---------------- = -------, written as cosec A
Perpendicular BC
Hypotenuse AC
(v) Secant A = -------------- = -------, written as sec A
Base AB
Base AB
(vi) Cotangent A = --------------- = -------, written as cot A
Perpendicular BC
Thus, the six trigonometrical ratios for an acute angle θ of a right triangle can be defined as –
Reciprocal Relations –
