Placing Circle Tangent to Two Lines (Illustrator)

I have a circle and I want it to perfectly kiss two lines of arbitrary angle in Adobe Illustrator:

How would I do that?

Answer

For a right (90°) angle:

Using Smart Guides (Ctrl/Cmd + U to toggle on/off)

_{Note. Make sure to turn off Snap to Point, Snap to Grid and Align Objects to Pixel Grid (so that it doesn't interfere with the Smart Guides)}

You would also go to Edit→Preferences→Smart Guides and manually add in the angle of your lines, if they aren't already a common angle (90:180)

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For an arbitrary angle:

Use this (free) tool/plugin for Illustrator by Astute Graphics called SubScribe which will accomplish this for other arbitrary angles (non 90° angles)

You use the Tangent Circle option

Select the point where the lines intersect and then drop the anchor based on how large you'd like the circle.