1)Following answer was obtained by me on another math help website which I reproduce here.
Wolfram
If you expand Taylor-series, you can immediately see it's a maximum, because there is no 1st-order correction and the 2nd-order correction is negative.
2) Following is the second answer, I got on internet , which I reproduce below:
The easiest way to visualise this since the circle is symmetric is to consider the simpler function
f(p) = p*e
-p, where p = (x
2 + y
2)
any plane section will have this form.
When p = 0.5 f(p) is approximately 0.3
When p =1, f(p) is approximately 0.4
When p = 2 f(p) is approximately 0.2
and f(p) is continuous so there is a max between p = (x
2 + y
2) = 0.3 and p = (x
2 + y
2) = 2