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This guide explores fundamental concepts related to circles, including radius, diameter, circumference, center, and various forms of circle equations. It explains the standard form of a circle equation, geometric and algebraic representations, and the impact of rotation on circle properties. Furthermore, it highlights the significance of eccentrics and the applications of circle geometry in fields like science and engineering, such as radar systems and seismology. Grasping these concepts is essential for a strong foundation in geometry.
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Circles Zach Laughman, Jesse Nelson, Brandon Wright, Samantha Huggins
Key Words • Radius- a straight line from the center to the circumference of a circle of sphere • Diameter- the distance from one end of circle to another • Circumference- the enclosing boundary of a circle -the distance around a circle • Start Angle- The angle in a circle at which you start to determine the degree of another angle • Center- the middle point of the circle
Diameter Radius Start Angle Center
Origin and Construction • Origin: a slice parallel to the base of a cone (see figure) • Construction: a circle is made up of points that are equidistance from the origin
Standard Form • (X-h)^2 + (Y-k)^2 = r^2 (0,0) • (X-0)^2 + (Y-0)^2 = r^2
Geometric/Algebraic Form • X^2 + Y^2 + aX + bY + c = 0 • Get this form into Standard Form by completing the square Complete the Square: • Get all X’s and Y’s on the left side • Get all constants on the right side • Take half of the middle number, square it, and add it to both sides (for X and Y) • Simplify
Rotated Form • When rotating a circle, the angle is the only part of the circle that changes • Same circle, rotated angle 90 degrees 135 degrees
Circle Relationships • An angle outside of the circle can be used to help find an angle within the circle • AxB = CxDA(A+E) = C(C+F) 4(4+6) = 3(3+x) B 10 6 E A 4 C 3 F X D 13.333
Conic Form • The conic form of a circle is formed when you intersect a double napped cone and a plane
Degenerate Case • The point as the radius approaches zero
Eccentricity • Says how round something is • The eccentricity of a circle is zero
Application • Science and Engineering • Radar systems, latitude/longitude, seismology (locating where an earthquake started)