Solve the diamond problem
21
22

Step-by-step explanation:

A quadratic equation is an equation with at least one squared term. The most common form of a quadratic equation is ax^2 + bx + c, where a, b, and c are coefficients (numbers). The graph of a quadratic equation is a parabola. If a in ax^2 + bx + c is positive, then the graph looks like a U-shape. However, if a is negative, the its graph looks like an upside-down U-shape.  

Here, the equation y=x^2-9 is a quadratic equation because it has the term x^2, which qualifies the requirement of having at least one squared term to be considered a quadratic equation. To find the root, simply set y = 0, i.e. set (x^2-9) = 0. This means x^2 = 9, which means x = 3 or x = -3. (these are the roots of y=x^2-9).