Points to Remember
· An equation involving trigonometric ratios of an angle is called a trigonometric identity if it is true for all values of the angle.
· Trigonometric identities
(i) sin 2 θ + cos2 θ = 1
(ii) 1 + tan 2 θ = sec2 θ
(iii) 1 + cot2 θ = cosec2 θ
· The line of sight is the line drawn from the eye of an observer to the point in the object viewed by the observer.
· The angle of elevation of an object viewed is the angle formed by the line of sight with the horizontal when it is above the horizontal level.
· The angle of depression of an object viewed is the angle formed by the line of sight with the horizontal when it is below the horizontal level.
· The height or length of an object or distance between two distant objects can be determined with the help of trigonometric ratios.