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### Straight line

In analytic geometry, a **straight line** can always be expressed as an equation of degree one in two unknowns

ax + by + c= 0

Such equations are known as *linear* equations.

##### Explanation

In school you learn to write the equation of a straight line as

y=ax+b

or as

y=mx+n

but of course that is all the same. You can also write the linear equation as

by=−ax −c

from which follows

In mathematics you use the notation that fits best. It is not a question of what is beautiful or what you usually do, but what is clear.