A right angled triangle is possible in a circle if the hypotenuse is the diameter of the circle
the perimeter is x +y+ d
write y in terms of diameter and x....by using pythagorans theorem
then differentiate and equate to zero ...
you would get the value of x in terms of d
now find the value of y using the found x and d....by pythagoran theorem...
then u will find that y and x are equal....