Graphics Reference
In-Depth Information
a
Fig. 10.17.
A segment of a circle defined by the angle
α
.
Y
m
c
X
Fig. 10.18.
The normal form of the straight line is
y
=
mx
+
c
.
where
m
is the slope and
c
the intersection with the
y
-axis, as shown in
Figure 10.18. This is called the
normal form
.
Given two points (
x
1
,y
1
)and(
x
2
,y
2
) we can state
y
−
y
1
x
y
2
−
y
1
x
2
−
=
(10.25)
−
x
1
x
1
which yields
x
1
)
y
2
−
y
1
y
=(
x
−
x
1
+
y
1
(10.26)
x
2
−
Although these equations have their uses, the more general form is much more
convenient:
ax
+
by
+
c
= 0
(10.27)
As we shall see, this equation possesses some interesting qualities.
