Finding a line through two points
Here's another demo using the Whiteboard
Given two points, we want to find the equation of the line that passes through both. The graph of a straight line is defined by two things: its slope and its intercept. The slope is quick to find from the two points-- just rise over run. So see how far it goes up (y2 - y1) and divide by how far it goes over (x2 - x1). Finding the intercept is a little bit trickier. The easiest way, once you know the slope, is to just use one of the points and slope you found. For example, plug in the numbers you know for x1, y1, and m into the equation:
y = mx+b
and solve for b. That's the intercept of your straight line equation. In this demo, the Whiteboard automatically calculates the slope of the line through the two points, but it's up to you to find the intercept. Try it now!