lesson

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Every time a basketball launches into the air, its flight path traces a symmetrical curve called a parabola.
You do not need to plot fifty coordinate pairs to draw this curve accurately; you only need to pinpoint four essential features.
πInteractive diagram
In the general quadratic form (or standard polynomial form), a quadratic function is written as y=ax2+bx+c, where a, b, and c are constants with aξ =0.
The sign of the leading coefficient a dictates global concavity: if a>0, the parabola opens upwards with a minimum turning point; if a<0, it opens downwards with a maximum turning point.
The easiest feature to find is the y-intercept, the point where the curve crosses the vertical y-axis by setting x=0, giving y=c.
Where does the curve cross the horizontal floor where height is zero?
Finding the X-Intercepts
The x-intercepts (or roots) are the locations where the curve hits the x-axis, which means setting y=0 and solving ax2+bx+c=0.
When a quadratic factorizes into (xβp)(xβq)=0, the zero-product principle states that at least one factor must equal zero, giving roots at x=p and x=q.
If it does not factor easily, the quadratic formula x=2aβbΒ±b2β4acββ finds the exact crossing points every time.
Performing a discriminant analysis with Ξ=b2β4ac reveals how the curve interacts geometrically with the x-axis.
If Ξ>0, there are two distinct real x-intercepts; if Ξ=0, the turning point is tangent to the x-axis (one repeated root); if Ξ<0, there are no real roots and the curve lies strictly above or below the axis.