Unit Circle Double Integral: Is 2π/3 the Answer?

[squenshl]

For the double integral \int\int_R sqrt(x^2+y^2) dx dy where R is the unit circle.
I got\int_0^\pi\int_1^1 sqrt(r²) r dr dtheta
Then after the integration I got an answer of 2pi/3 as my final answer.
Is this right.
The bottom of the 2nd integral is -1 not 1

 

[tiny-tim]

For the double integral \int\int_R sqrt(x^2+y^2) dx dy where R is the unit circle.
I got\int_0^\pi\int_1^1 sqrt(r²) r dr dtheta
Then after the integration I got an answer of 2pi/3 as my final answer.
Is this right.
The bottom of the 2nd integral is -1 not 1

Hi squenshl!

(have a pi: π and a theta: θ and try using the X² tag just above the Reply box )

(and you needed \int_{-1}^1)

erm … you can't have r less than 0! ​