00:01
All right, using this diagram, we're asked to find what the radius is here.
00:04
And they tell us this is a perpendicular line and the ab is a tangent.
00:08
And so we're just going to use the pythagorean theorem here.
00:10
So we have a squared plus b squared equals c squared.
00:16
And so for a, we can use nine, so nine squared.
00:20
And then for b is r squared.
00:23
And then for c, we have six plus r.
00:26
So we have to do six plus r in parentheses squared.
00:30
And so this will be 81 plus r squared.
00:34
And remember, you've got to foil this...
