Andrewww 3 years ago Your friend, Patricia, is having a hard time understanding the concept behind the domain and range of a parabola. Using complete sentences, explain the meaning of the domain and range of the graph of y = -x2 + 4x - 21 and how to find both. Keep in mind, your goal is to help Patricia understand the "concepts", not just how to use the steps.

1. gandalfwiz

The domain is all the possible x values that exist in the graph. On the graph -x^2 +4x-21, no matter which x value you choose, there is a corresponding y value. Even if your x is infinity, negative infinity, or zero, the parabola exists there, so your domain is "all real numbers."

2. Andrewww

thank you so so so much but i need the range too

3. gandalfwiz

The range is all the possible y values. In the above said parabola, the highest is ever reaches is -17. The graph just doesn't exist higher than that. So the range is "all real numbers less than or equal to -17."

4. gandalfwiz

*highest it ever reaches*, sorry