Use the intercept form of the equation of a parabola, y=a(x-p)(x-q).
y=2.25(x+16)(x+2)
Practice makes perfect
We want to write the equation of the parabola that passes through the point (- 18,72) and has x-intercepts - 16 and - 2. To do so, we will use the intercept form of a quadratic function.
y=a(x-p)(x-q)
In this form, p and q are the intercepts. Therefore, we can partially write our equation.
y=a(x-(- 16))(x-( - 2))
⇕
y=a(x+16)(x+2)
Finally, since the parabola passes through the point (- 18,72), we can substitute - 18 for x and 72 for y in our partial equation to solve for a.
