Download Unit 2 Equation of a Circle

Unit 2
Equation of a Circle
Learning Goal: I can use what I
know about Pythagorean Theorem
to determine the equation of a
circle in x2 + y2 = r2 form.
Equation of a Circle
• Recall: Pythagorean Theorem: a2 + b2 = c2
• By choosing a point on the circle, a and b become x
and y and the radius of the circle is the hypotenuse.
x2 + y2 = r2
*Equation is only valid for circles
centered around the origin
Example 1
• Given the circle x2 + y2 = 16
a) State the radius
b) Sketch the graph
c) State the intercepts
Example 2
• (3, -5) is on the circumference of a circle having a
centre (0,0).
a) Find the radius
b) Find the equation of the circle
Example 3
• A satellite orbits Earth on a path with equation x2 + y2 =
450 000 000. Another satellite, in the same plane, is
currently located at (12 504, 16 050). Is the second
satellite inside or outside the orbit of the first satellite?
Explain.
Homework
• Pg. 155-156 # 1ad, 2ad, 3, 4, 8, 9