x^2=a^2-ax

The formula of X 2+ax = a 2 is (x+a/2) 2-(a/2) 2 = a 2.

There is (x+a/2) 2 = 5a 2/4, there is x=(a* root number 5)/2-a/2=a* (root number 5- 1)/2, and the other solution is negative, so I give up!