X = 20\Y --> X^2 = 400 \ Y^2
400 \ Y^2 ) - Y^2 = 9
400 - Y^4 = 9Y^2
Y^2 = A
400 - A^2 = 9A
-A^2 - 9A + 400 = 0
D = 81 -4*(-1)*400 = 81 + 1600 = 1681 ; V D = 41
A1 = ( 9 + 41 ) \ - 2 = 50 \ - 2 = ( - 25)
A2 = ( - 32 ) \ (- 2 ) = + 16
X^2 = A
X = V A
X1 = V ( -25 ) - не может быть по по определению
X2 = V 16 = 4