Question

This is the graph of y = -x2 - 2x + 8. What is the range of this function?

Answer 1

Hi there!

$\large\boxed{(-\infty, 9)}$

We can find the range using completing the square:

y = -x² - 2x + 8

Factor out a -1:

y = -(x² + 2x) + 8

Use the first two terms. Take the second term's coefficient, divide by 2, and square:

y = -(x² + 2x + 1) + 8  

Remember to add by 1 because we cannot randomly add an additional number into the equation:

y = -(x² + 2x + 1) + 8 + 1

Simplify:

y = -(x + 1)² + 9

Since the graph opens downward (negative coefficient), the range is (-∞, 9)