Page:Elements of the Differential and Integral Calculus - Granville - Revised.djvu/166


 * Differentiate with respect to the time.


 * Make a list of the given and required quantities.


 * Substitute the known quantities in the result found by differentiating (third step), and solve for the unknown.

EXAMPLES

1. A man is walking at the rate of 5 miles per hour towards the foot of a tower 60 ft. high. At what rate is he approaching the top when he is 80 ft. from the foot of the tower?



2. A point moves on the parabola $$6 y = x^2$$ in such a way that when x = 6, the abscissa is increasing at the rate of 2 ft. per second. At what rates are the ordinate and length of arc increasing at the same instant?