Reflections, Stretches, and Shrinks
Parabolas can do more than just move around—they can flip and change shape too! When you put a negative sign in front of the entire function (-f(x) = -x²), the parabola reflects over the x-axis, flipping upside down.
Interestingly, replacing x with -x in f(x) = x² doesn't change the parabola's appearance. This is because −x² = x², making the parabola symmetrical about the y-axis.
You can stretch or shrink a parabola horizontally by replacing x with ax. When 0 < a < 1 (like ½), the parabola stretches wider. When a > 1 (like 2), it shrinks narrower. For example, f(2x) = (2x)² creates a narrower parabola than the original.
For vertical stretches and shrinks, multiply the entire function by a constant a. When a > 1, the parabola stretches taller; when 0 < a < 1, it shrinks shorter. So 3x² is stretched vertically compared to x², while ½x² is shrunk.
Remember: Horizontal transformations work oppositely from what you might expect—multiplying by a smaller fraction (like ½) makes the parabola wider, not narrower!