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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 : 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 : Definition & Construction of a Parabola (Part 1)

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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 symmetry 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 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.

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

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

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

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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 »)

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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).

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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

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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

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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.

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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.

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

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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 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.

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Y = ½ x 2 Y = - ¼ x 2 Definition & Construction of a Parabola (Part 1) II- Geometric Properties : Graphs

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Second degree Functions

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Definition & Construction of a Parabola (Part II)

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Parabola The set of all points that are equidistant from a given point (focus) and a given line (directrix).

Parabola The set of all points that are equidistant from a given point (focus) and a given line (directrix).

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