Hello, jmailloux!

You did it again . . . you made the wrong part.

A 1.7-m tall man walks away from a 9-m high streetlight at 0.8 m/s.

How fast is *the end of his shadow* moving when he is 20 m from the lamppost? Code:

*
| *
| *
9 | | *
| 1.7| *
| x | s-x *
----*-----------+-----------------------*----
: - - - - - - - - s - - - - - - - - :

This time, we make be the *entire* distance,

. . from the lampost to the end of his shadow.

From the similar right triangles, we have: .

Then: .

Differentiate with respect to time: .

Since