Answer:
y = √(900 -x²); see below for a graph
Step-by-step explanation:
The high point (30 ft) is the radius of the circle, so the equation is ...
x² +y² = 30²
Subtract the x-term and take the square root to find y.
y² = 30² -x²
y = √(30² -x²) = √(900 -x²)
The graph is shown in the attachment.
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<em>Comment on "how that website works"</em>
We don't know what web site you're referring to, but the one I like is Desmos. It only takes a few minutes to learn to graph the equation here.
You don't even need to solve for y to get the desired graph. You can simply specify that y ≥ 0.