Equation of a Parabola

CONCEPTS

Parabola Equation

• y = k (x–a)² + b

• k > 0 or k < 0 = opens up/down

• k = "width" or "openness"

• a = shift left–to–right & x coordinate of vertex

• b = shift up & down & y coordinate of vertex

• y – intercept when x=0

PRACTICE PROBLEMS

Question 1 Graph the parabola 9x² - 9y = 81

-- Answer -- Put the equation into the form, y = k (x-a)² + b

- 9y = 81 - 9x²

y = -9 +x²

y = -9 + x² = x² - 9

ACT PRACTICE PROBLEMS