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Conic Sections: Eccentricity To each conic section (ellipse, parabola, hyperbola, circle) there is a number called the eccentricity that uniquely characterizes the shape of the curve. Conic Sections: Eccentricity If e = 1, the conic is a parabola. If e = 0, the conic is a circle. If e < 1, the conic is an ellipse. If e > 1, the conic is a hyperbola. Conic Sections: Eccentricity For both an ellipse and a hyperbola c e a where c is the distance from the center to the focus and a is the distance from the center to a vertex. Classifying Conics 10.6 What is the general 2nd degree equation for any conic? What information can the discriminant tell you about a conic? The equation of any conic can be written in the form2 2 Ax Bxy Cy Dx Ey F 0 Called a general 2nd degree equation Circles ( x 1) ( y 2) 16 2 2 Can be multiplied out to look like this…. x y 2 x 4 y 11 0 2 2 Ellipse ( x 1) 2 ( y 1) 1 4 2 Can be written like this….. x 4 y 2x 8 y 1 0 2 2 Parabola ( y 6) 4( x 8) 2 Can be written like this….. y 12 y 4 x 4 0 2 Hyperbola ( y 4) ( x 4) 1 9 2 2 Can be written like this….. 9 x y 72 x 8 y 1 0 2 2 How do you know which conic it is when it’s been multiplied out? • Pay close attention to whose squared and whose not… • Look at the coefficients in front of the squared terms and their signs. Circle Both x and y are squared And their coefficients are the same number and sign x y 2 x 4 y 11 0 2 2 Ellipse • Both x and y are squared • Their coefficients are different but their signs remain the same. x 4 y 2x 8 y 1 0 2 2 Parabola • Either x or y is squared but not both y 12 y 4 x 4 0 2 Hyperbola • Both x and y are squared • Their coefficients are different and so are their signs. 9 x y 72 x 8 y 1 0 2 2 1. x 2 4y 2 2x 3 0 2. 2x 2 20x y 41 0 You Try! 1. Ellipse 2. Parabola 3. 5x 2 3y 2 30 0 3. Hyperbola 4. x 2 y 2 12x 4y 31 0 4. Circle 5. x 2 y 2 6x 6y 4 0 5. Hyperbola 6. x 2 8x 4y 16 0 7. 3 x 3 y 30 x 59 0 2 2 8. x 2 y 8 x 7 0 2 2 9. 4 x y 16 x 6 y 3 0 2 2 10. 3 x y 4 y 3 0 2 2 6. Parabola 7. Circle 8. Ellipse 9. Hyperbola 10.Ellipse When you want to be sure… of a conic equation, then find the type of conic using discriminate information: Ax2 +Bxy +Cy2 +Dx +Ey +F = 0 B2 − 4AC < 0, B = 0 & A = C B2 − 4AC < 0 & either B≠0 or A≠C B2 − 4AC = 0 B2 − 4AC > 0 Circle Ellipse Parabola Hyperbola Classify the Conic 2x2 + y2 −4x − 4 = 0 Ax2 +Bxy +Cy2 +Dx +Ey +F = 0 A=2 B=0 C=1 B2 − 4AC = 02 − 4(2)(1) = −8 B2 − 4AC < 0, the conic is an ellipse Graph the Conic 2x2 + y2 −4x − 4 = 0 Complete the Square 2x2 −4x + y2 = 4 2(x2 −2x +___)+ y2 = 4 + ___ (−2/2)2= 1 2(x2 −2x +1)+ y2 = 4 + 2(1) 2(x−1)2 + y2 = 6 2( x 1) y 1 6 6 2 2 ( x 1) y 1 3 6 V(1±√6), CV(1±√3) 2 2 Steps to Complete the Square 1. Group x’s and y’s. (Boys with the boys and girls with the girls) Send constant numbers to the other side of the equal sign. 2. The coefficient of the x2 and y2 must be 1. If not, factor out. 3. Take the number before the x, divide by 2 and square. Do the same with the number before y. 4. Add these numbers to both sides of the equation. *(Multiply it by the common factor in #2) 5. Factor Write the equation in standard form by completing the square 2 x 4 y 2x 8 y 1 0 2 1 2 2 x 2 x 4( y 2 y) 1 2 2 2 x 2 x ___ 4( y 2 y ___) 1 ___ ___ 2 2 ( x 2 x 1) 4( y 2 y 1) 1 1 (4)(1) 2 2 ( x 1) 4( y 1) 4 2 2 ( x 1) 2 4( y 1) 2 4 4 4 4 2 2 ( x 1) ( y 1) 1 4 1 What is the general 2nd degree equation for any conic? Ax Bxy Cy Dx Ey F 0 2 2 What information can the discriminant tell you about a conic? B2- 4AC < 0, B = 0, A = C Circle B2- 4AC < 0, B ≠ 0, A ≠ C Ellipse B2- 4AC = 0, Parabola B2- 4AC > 0 Hyperbola Assignment 10.6 Page 628, 29-55 odd