A ladder 13m long leans against a wall. The foot of the ladder is pulled along the ground away from the wall, at the rate of 1.5m/sec. How fast is the angle `theta` between the ladder and the ground is changing when the foot of the ladder is 12m away from the wall.

Explanation

`tan theta = y/x`

`sin theta = y/13`

differentiating wrt t

`cos theta* (d theta)/dt = ((dy)/dt)/13`

`12/13*(d theta)/dt = (dy/dt)/13`

`(d theta)/dt = (dy/dt)/12` eqn (1)

now, `x^2 + y^2 = 13^2`

`2xdy/dt + 2ydy/dt = 0`

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