1 answer
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I don't see any "figure below" , but I can surmise your figure shows a quarter circle in the first quadrant with a rectangle, whose base is along the x-axis, its height along the y-axis and it touches the quarter circle at (x,y)
Area = xy
= x√(36-x^2) or x(36-x^2)^(1/2)
for the domain, we have to make sure that the number under the √ does not become negative, so
0 < x < 6
Meaning the answer is D