JST17 5. Section 1f Equation of a line from gradient and a point

Use the slider to set the gradient of the line, which will pass through the green point (which you can move). Use the checkbox to see the line. Can you explain why the equation [math]y-y_{1} = m(x - x_{1})[/math] gives the equation of the line?
– Jill Stephenson, Integral Resources

Information: JST17 5. Section 1f Equation of a line from gradient and a point