What if your equation has a negative a? Like y = -3x² + 6x + 1. No sweat. a = -3, b = 6.
So x = -(6) / (2 * -3). That’s x = -6 / -6, which is x = 1. Negative divided by negative? Positive vibes only.
And if b is zero? Like y = 5x² + 0x − 2? Then x = 0. The axis is the y-axis itself. How convenient is that?
A Little Trick for the Forgetful
If you blank on the formula—don’t panic. You can also find the vertex by completing the square. But that’s like baking bread from scratch when you have a bread machine. Use the formula.
Another trick? If you’ve already got two x-intercepts (where the parabola crosses the x-axis), the axis is the exact midpoint between them. Add ‘em up, divide by two. That’s literally the average. You got this.
