The first step to solve a quadratic equation that's set to zero is to factor the quadratic equation:

z² - 9 = 0
(z - 3)(z + 3) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (z - 3) or (z + 3) must equal zero:

If (z - 3) = 0, z must equal 3
If (z + 3) = 0, z must equal -3

So the solution is that z = 3 or -3

A circle is a figure in which each point around its perimeter is an equal distance from the center. The radius of a circle is the distance between the center and any point along its perimeter. A chord is a line segment that connects any two points along its perimeter. The diameter of a circle is the length of a chord that passes through the center of the circle and equals twice the circle's radius (2r).

The Pythagorean theorem defines the relationship between the side lengths of a right triangle. The length of the hypotenuse squared (c²) is equal to the sum of the two perpendicular sides squared (a² + b²): c² = a² + b² or, solved for c, \(c = \sqrt{a + b}\)

A cube is a rectangular solid box with a height (h), length (l), and width (w). The volume is h x l x w and the surface area is 2lw x 2wh + 2lh.

An acute angle measures less than 90°, a right angle measures 90°, and an obtuse angle measures more than 90°.