# The specification of a straight lineWhat is the specification of a straight line?

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A straight line is one that has an equation with x and y values having a one to one correspondence. It should not be possible to achieve the same y value for more than one x value or vice-versa. This gives the general equation of a straight line as ax + by + c = 0.

A straight line may be specified in many ways.

One way is to specify the coordinates of 2 points in Cartesian plane.

(x1,x2) and (y1,y2).

The equation of the line is:

y - y1 = (y2-y1)*(x-x1)/(x2-x1)

Another way is by giving its slope and the coordinates of one point located on the line. Conclusion: Through any point there is exactly one straight line with a given slope.

The equation of the line is:

y = mx + n

m is the slope and (x1,y1) is the point.

y - y1 = m(x - x1)