I have the following...
∫30∫1x/3fdydx
I need to rewrite this in polar coordinates. I graphed the triangle and can see that...
tan(θ)=13
But I do not know how to use this information to rewrite my integral into polar coordinates using π.
Answer
For simplicity, I will assume that f(x,y)=1.
Note that if you are given f(x,y) explicitly, you have to re-express f(x,y) in terms of r and θ.
Using the hint that x=rcosθ as mentioned in the comment section, and y=1,
1=rsinθ⟹r=1sinθ
Also,
tan(θ)=13⟹θ=arctan(13)
So we can setup the double integral as the following,
∫π2arctan(13)∫1sinθ0r drdθ
Below is a (ugly drawn) picture for a fixed (r,θ).
(Another exercise) Rewrite the double integral in polar coordinates
∫30∫x/30 dydx
Let x=3,
3=rcosθ⟹r=3cosθ
Also, tan(θ)=13⟹θ=arctan(13)
So we can setup the double integral as the following,
∫arctan(13)0∫3cosθ0r drdθ
Below is another (ugly drawn) picture for a fixed (r,θ).
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