Differentiation - Differentiation of Trigonometric, Logarithmic and Exponential Functions - General

A \(2\) metres ladder was placed against a vertical wall. The ladder started to slide downwards, at a constant decreasing rate of \(4\) cm/s, with the top and bottom of ladder remained in contact with the vertical wall and horizontal ground. Find the rate of change of the angle between the ladder and the horizontal when bottom of the ladder is \(1.3\) metres away from the wall.