Geometry Course/Line/Straight Line

Straight Line
Straight Line is a line that can be drawn from any 2 points

Straight Line through 2 points
If there are 2 points (x1,y1) and (x,y) a line can be drawn these two points with a slope
 * $$m = \frac{y-y_1}{x-x_1} $$

The equation of the line can be
 * $$y = y_1 + m (x - x_1)$$

Straight Line through point
From above if x1 and y1 equal zero then
 * y = x

Equation of a straight line through point (0,0) that has a slope equal 1