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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.