00:01
Hi, in this problem we have to evaluate i equal to double integral over r square, that is minus infinity to infinity, minus infinity to infinity of e to the power minus x square plus y square bx divide.
00:27
Now we can put x square plus y square to be equal to r square.
00:34
And here, theta varies from 0 to 2 pi and r varies from 0 to infinity.
00:49
And d x, dx, dy is equal to r, drd theta.
01:00
This implies r i is equal to integral 0 to 2 pi, 0 to infinity, e to the par minus r square rdr d theta.
01:23
Now putting r square equal to t, we get 2rdr equal to d t, which implies i is equal to 0 to 2 pi.
01:50
Now when r is equal to 0, t will also be equal to 0 and when r is equal to infinity t will also be infinity therefore this will be equal to e to the part minus t d t by 2 d theta now this is equal to integral 0 to 2 pi half e to the power minus t and minus of that because derivative of minus t is minus 1 limit 0 to infinity d theta now this is equal to 0 to 5 pi half minus limit as t approaches infinity, e to the power minus t, d theta...