Reveal Exercise. An isosceles triangle has side lengths , r and 2. The angle between the sides of length r is . If r is increasing at a rate of 3 units whenr = 2, then at what rate is the angle changing at that time? SOLUTION: The given rate is di 3 units units The rate to be determined is de Draw a picture. It should be clear from your picture that r and 8 satisfy the relation Differentiating implicitly with respect to time, ? cos( ?)