1.NounAny function whose graph is a straight line:
f
(
x
)
=
a
x
+
b
{\displaystyle f(x)=ax+b}
2.NounAny function whose value on the sum of two elements is the sum of the values of the function on the two elements and whose value on the product of a scalar times an element is the scalar times the value of the function on the element:
f
(
a
x
+
b
y
)
=
a
f
(
x
)
+
b
f
(
y
)
{\displaystyle f(ax+by)=af(x)+bf(y)}