# Write an equation of a line given one point

The more we go down in this situation, for every step we move to the right, the more downward sloping will be, the more of a negative slope we'll have. Point-Slope Form Parallel, Perpendicular Lines Purplemath Straight-line equations, or "linear" equations, graph as straight lines, and have simple variable expressions with no exponents on them.

So this is our y-intercept. So this would be a negative over a positive, it would give you a negative number. Now, they tell us what the slope of this line is. So y is equal to 0 plus b, or y will be equal to b, when x is equal to 0. This is great for graphingand can be quite useful for word problems. They've given me the value for m, along with values for an x and a y.

### Equation of a line formula

The following video shows how to write the equation for a line given its slope and a point on the line. The slope of a vertical line is undefined, and regardless of the y-value of any point on the line, the x-coordinate of the point will be c. The y-intercept just tells us where we intercept the y-axis. So hopefully, we're a little familiar with the slope already. If our run is positive, our rise here is negative. If you see an equation with only x and y — as opposed to, say x2 or sqrt y — then you're dealing with a straight-line equation. Just plug in your x-value; the equation is already solved for y. So the only thing I don't have so far is a value for is b which gives me the y-intercept. Nowadays, you likely needn't worry too much about the "standard" forms; this lesson will only cover the more-helpful forms.
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