# Lesson 1. 3D Coordinate Systems 1 Today... ```SM223 – Calculus III with Optimization
Asst. Prof. Nelson Uhan
Fall 2012
Lesson 1. 3D Coordinate Systems
1
Today...
● 3D rectangular coordinate system
● Distance formula in 3D
○ Equation for a sphere
● Graphing equations in 3D
2
3D rectangular coordinate system
● How do we locate points in space?
● 3 mutually perpendicular coordinate axes through origin O:
z
O
y
x
● 3 coordinate planes
○ x y-plane contains the
○ xz-plane contains the
○ yz-plane contains the
● The coordinate planes divide space into 8 octants
○ The first octant is the octant with positive axes
1
● Any point P in space can be represented an ordered triple (a, b, c):
z
(0, b, c)
(a, 0, c)
P(a, b, c)
a
c
O
y
x
b
(a, b, 0)
● (a, b, c) are the rectangular coordinates of P (also known as Cartesian coordinates)
○ a is called the x-coordinate of P
○ b is called the y-coordinate of P
○ c is called the z-coordinate of P
● (a, b, 0) is the projection of P(a, b, c) on the
● (0, b, c) is the projection of P(a, b, c) on the
● (a, 0, c) is the projection of P(a, b, c) on the
● We often refer to three-dimensional space as R3
Example 1.
(a) Plot P(3, −1, 2).
z
y
x
(b) What is the projection of P onto the x y-plane?
2
3
Distance formula in 3D
● The distance between two points P1 (x1 , y1 , z1 ) and P2 (x2 , y2 , z2 ) is
Example 2. What is the distance from the point P(2, −1, 0) and Q(4, 1, 1)?
● A sphere is the set of all points P(x, y, z) whose distance from a center C(h, k, l) is radius r
○ The standard equation for a sphere with radius r and center (h, k, l) is
Example 3. Show that x 2 + y2 + z 2 − 2x − 4y + 8z = 15 represents a sphere, and find its center and radius.
4
Graphing equations in 3D
Example 4. Which points (x, y, z) satisfy y = 2 in R3 ?
z
y
x
3
Example 5.
(a) Draw y = x 2 in R3 .
z
y
x
(b) Draw y = x 2 , z = 2 in R3 .
z
y
x
Example 6. Give an equation for the
● xz-plane:
● x y-plane:
● yz-plane:
4
```
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