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Definition & Construction of a Parabola (Part 1)

Definition & Construction of a Parabola (Part 1). Let f be the function defined by : (a≠0) I - Algebraic properties : 1°) Even function : for any x  R, f(-x) = f(x) . 2°) Rate of growth not constant :

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Definition & Construction of a Parabola (Part 1)

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  1. Definition & Construction of a Parabola (Part 1) Let fbe the function defined by : (a≠0) I - Algebraic properties : 1°) Even function: for any x  R, f(-x) = f(x). 2°) Rate of growth not constant : 3°) Sign of T = Sign of a on [0 ; +∞[ , and Sign of T = Sign of (-a) on ]- ∞ ; 0] 4°) Chart of the Variations of f :

  2. Definition & Construction of a Parabola (Part 1)II- Geometric Properties : 1°) The curve has (Oy) as an axis of symmetry. For that reason the curve is called a Parabola. 2°) The Parabola is tangent to the (Ox) Axis in O. 3°) The Parabola passes through the point A(1 ; a). 4°) If a > 0 the Parabola concavity is directed towars the positive y : (as one can say the « the bowl can hold water ») If a < 0 the Parabola concavity is directed towards the negative y : (as one can say the « the bowl cannot hold water ») 5°) The Parabola intercepts the 1st bisector line (y = x) at point B(1/a ; 1/a) 6°) On B the Parabola is tangent to the line joining B to the middle of the segment located under the tangent, which is the point of abscissa 1/2a 7°) By symmetrywith respect to Oy we get the points A’(-1 ;a) and B’(-1/a ; 1/a) 8°) If a is very small compared to the unity (a << 1) , the parabola is widely opened, inverselyif a >>1 the parabola is very narrow around the axis of symmetry. 9°) The parabola contains absolutely no piece of a straight line. 10°) The branches spread indefinitely in the direction of the Oy axis.

  3. Definition & Construction of a Parabola (Part 1)II- Geometric Properties : 1°) The Parabola is symmetrical through the (Oy ) axis. It was named so because of that property.

  4. Definition & Construction of a Parabola (Part 1)II- Geometric Properties : 2°) The Parabola is tangent to the (Ox) Axis in O (0;0).

  5. Definition & Construction of a Parabola (Part 1)II- Geometric Properties : 3°) The Parabola passes through the point A(1 ; a).

  6. Definition & Construction of a Parabola (Part 1)II- Geometric Properties : 4°) If a > 0 the Parabola concavity is directed towars the positive y : (as one can say the « the bowl can hold water ») If a < 0 the Parabola concavity is directed towards the négative y : (as one can say the « the bowl cannot hold water »)

  7. Definition & Construction of a Parabola (Part 1)II- Geometric Properties : 5°) The Parabola intercepts the 1st bisector line (y = x) at point B(1/a ; 1/a).

  8. Definition & Construction of a Parabola (Part 1)II- Geometric Properties : 6°) On B (1/a;1/a) the Parabola is tangent tothe line joining B to the middle of the segment located under the tangent,which is the point of abscissa 1/2a

  9. Definition & Construction of a Parabola (Part 1)II- Geometric Properties : 6°) On B (1/a;1/a) the Parabola is tangent to the line joining B to the middle of the segment located under the tangent, which is the point of abscissa 1/2a

  10. Definition & Construction of a Parabola (Part 1)II- Geometric Properties : 8°) If a is very small compared to the unity (a << 1) , the parabola is widely opened, Inversely if a >>1 the parabola is very narrow around the axis of symmetry.

  11. Definition & Construction of a Parabola (Part 1)II- Geometric Properties : 9°) The parabola contains absolutely no piece of a straight line.Because the rate of growth is never constant.

  12. Definition & Construction of a Parabola (Part 1)II- Geometric Properties : 10°) The branches spread indefinitely in the direction of the Oy axis.

  13. Definition & Construction of a Parabola (Part 1)II- Geometric Properties : (summary) 1°) The curve has (Oy) as an axis of symmetry. For that reason the curve is called a Parabola. 2°) The Parabola is tangent to the (Ox) Axis in O. 3°) The Parabola passes through the point A(1 ; a). 4°) If a > 0 the Parabola concavity is directed towars the positive y : (as one can say the « the bowl can hold water ») If a < 0 the Parabola concavity is directed towards the négative y : (as one can say the « the bowl cannot hold water ») 5°) The Parabola intercepts the 1st bisector line (y = x) at point B(1/a ; 1/a) 6°) On B the Parabola is tangent to the line joining B to the middle of the segment located under the tangent, which is the point of abscissa 1/2a 7°) By symetry with respect to Oy we get the points A’(-1 ;a) and B’(-1/a ; 1/a) 8°) If a is very small compared to the unity (a << 1) , the parabola is widely opened, inverselyif a >>1 the parabola is very narrow around the axis of symmetry. 9°) The parabola contains absolutely no piece of a straight line. 10°) The branches spread indefinitely in the direction of the Oy axis.

  14. Definition & Construction of a Parabola (Part 1)II- Geometric Properties : Graphs Y = ½ x2 Y = - ¼ x2

  15. Second degree Functions

  16. Definition & Construction of a Parabola (Part II)

  17. Definition & Construction of a Parabola (Part II)

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