A linear function of one variable is one whose graph is a straight line. In general, a linear function can be a function of one or more variables. Each term in a linear function is a polynomial of degree one in one of the variables, or a constant. So ()=3+2
f
(
x
)
=
3
x
+
2
is a linear function.
A linear equation has an equals sign, with linear functions on both sides. You can always move everything to one side of the equation, so solving a linear equation is essentially finding the zero of some linear function. 3+2=0
3
x
+
2
=
0
is a linear equation. A little algebra yields =−23.
x
=
−
2
3
.
It does get murky because the notation is overloaded. Consider =3+2.
y
=
3
x
+
2.
We normally think of that as a function of a single variable
x
, pretty much just an abbreviation for ()=3+2
f
(
x
)
=
3
x
+
2
. But it’s also a linear equation in two variables
x
and .
y
.
That equation’s solutions are the zeros of the linear function of two variables (,)=3−+2
g
(
x
,
y
)
=
3
x
−
y
+
2
.
