I will choose the symbol * to expess square
(x)*+(X+3)*=(x+6)*
x*+(X*+6x+9)=x*+12x+36)
2x*+6x+9=x*+12x+36
2x*-x*+6x-12x+9-36=0
x*-6x-27=0
factor this:
(x+3) (x-9)=0
(x+3)=0 x=-3 NO
(x-9) x=9 YES
SMALL SIDE 9
MEDIAN 9+3=12
HYPOTENUSE 9+6=15
9*+12*=15*
81+144=225
225=225