### Home > CALC3RD > Chapter Ch7 > Lesson 7.2.2 > Problem 7-66

7-66.

Remember Eric and the *tip* of his shadow moving away from the lamppost? Draw a diagram before you start this problem.

Use similar triangles to write an equation relating the proportional sides.

Use implicit differentiation to convert the geometric equation into a rate equation.

In other words, find the derivative of everything in terms of time, .