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Exercise 1076Calculus › Multivariable calculus › Multiple integralsL1Added 3 Nov 2026

Polar integral over a half-disk

#polar#half-disk#integral

Statement

Compute I=∬Dx2+y2 dx dy\displaystyle I=\iint_D\sqrt{x^2+y^2}\,dx\,dy where DD is the disk of radius 11 centered at (0,0)(0,0) intersected with the half-plane y≥0y\ge0.

Hint

Polar: 0≤r≤10\le r\le1, 0≤θ≤π0\le\theta\le\pi.

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Solution

Polar.
I=∫0π∫01r⋅r dr dθ=π⋅13=π3.I=\int_0^\pi\int_0^1 r\cdot r\,dr\,d\theta=\pi\cdot\frac{1}{3}=\frac{\pi}{3}.

Conclusion. I=π/3I=\pi/3.