Assume I have points $(125,1)$ and $(5000,20)$. The slope would be $m = \frac{y_2 - y_1} { x_2 - x_1}$ or $256.5789474$, right?
Assume the slope and one point are known, I should be able to compute the y value for a given $x$ using the point slope formula $y - y_1 = m (x - x_1)$, right? Using the example above, say I have point $(125,1)$ and a slope of $256.5789474$, what would be $y$ value when $x = 5000$? Should be $20$, right? $$y - y_1 = m (x - x_1) $$ $$y = m (x - x_1) + y1$$ $$ y = 256.5789474 (5000 - 125) + 1$$ $$ y = 1250823.36857$$
What did I do wrong?
Also, are there any online interactive graphing tools that display a slope and allow the user to interact with it to see the different values of $y$ for a given $x$?