How to determine if a point is inside a 2D convex polygon?

Question

I have a convex polygon (typically just a rotated square), and I know all of 4 points. How do I determine if a given point (yellow/green) is inside the polygon?

Answer 1

Check to see if it's on the same side of the 4 half-planes defined by the lines that contain the line segments that make up the sides of the quad.

Here is a good explanation.