Use similar triangles to explain why the slope *m *is the same between any two distinct points on a non-vertical line in the coordinate plane; derive the equation *y *= *mx *for a line through the origin and the equation *y *= *mx *+ *b *for a line intercepting the vertical axis at *b*.

**8.EE Expressions and Equations**

**8.EE.B** *Understand the connections between proportional relationships, lines, and linear equations.*