# Math Help - double integral

1. ## double integral

can someone help me with this double integral please.

DOUBLE INTEGRAL: e^-r^2 r dr dtheta
where r is bounded by 0 and a
and theta is bounded by 0 and pi/2

thanks

2. Hello, mesterpa!

It seems to be easy enough . . .

Can someone help me with this double integral please.

∫∫ e^{-r²} r dr dθ

. . where r is bounded by 0 and a
. . and θ is bounded by 0 and π/2

The inner integral is: .
e^{-r²} r dr

Let: u = -r² . . du = -2r dr

And we have: .
e^u du .= .-½ e^u . . -½e^{-r²}

Now evaluate for r = 0 to r = a.

Then integrate with respect to θ and evaluate.

3. hi. thanks for your help.
sorry my experience of integration is very little.
could you tell me which method if integration this is being used.
thanks