## Online Course Discussion Forum

### Math II-B Week 9 Homework

In question 9.22, I don't understand what it means by the fifth ball "resting" one inch off the ground.

The setup for 9.22 is similar to 9.4, which I think was just briefly discussed during the live session.

For both of these problems, four identical balls with radius 1 are glued to the ground and a fifth ball is stacked on top of them (resting in the middle of them).

In 9.22 the radius of the fifth ball isn't given. What is given is that the ball rests 1 inch off the ground, meaning that the distance from the bottom of the fifth ball to the ground is 1 inch.

Hopefully this helps visualizing a little bit. The Wikipedia page here is a slightly different topic, but could also be helpful for visualizing the stacked spheres.

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