Find the volume under the surface with several constraints

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I need to find the volume under the surface $$z = a^2 - x^2$$ on domain restricted by these surfaces and planes: $$y = 2x$$ $$x+y=a$$ $$z = 0$$ $$y=0$$

I made a drawing but I cannot even infer what the bounds of integration are. When I drew all these lines (assuming $a=2$) I got this: enter image description here

What are the bounds of integration in this case?

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There are 2 best solutions below

6
On

To find the limit we need to make a sketch of the surface and bounds in the planes $z-x$ and $y-x$.

enter image description here

From here it follows that the volume is given by the sum of the following integrals

$$\int_{-a}^{0}\,dx\int_{0}^{-x+a} (a^2-x^2) \,dy $$

$$\int_{0}^{a/3}\,dx\int_{2x}^{-x+a} (a^2-x^2) \,dy $$

$$\int_{a/3}^{a}\,dx\int_{-x+a}^{2x} (a^2-x^2) \,dy $$

12
On

The integration will have to be done in two parts. As can be seen from the graph (Desmos representation:https://www.desmos.com/calculator/mktcqyonrj) a triangular region is formed between y=0, y=2x and y=a-x. Hence the integrals obtained would be: $$\int_0^{a/3} \int_0^{2x} \int_0^{a^2-x^2} \,dz,dy,dx$$

$$\int_{a/3}^a \int_0^{a-x} \int_0^{a^2-x^2} \,dz,dy,dx$$

The sum of these integrals should give you the total volume.

a better graph

In the graph, if you can imagine it, CFH is the surface we are looking for. We need to calculate the volume beneath this surface and above z=0.