{xy=5 {x2+y2=26 решите как биквадратное

Х = 5 / у
Х^2 = 25 / у^2
Х^2 = 26 - у^2
25 / у^2 = 26 - у^2
25 = у^2( 26 - у^2 )
25 = 26у^2 - у^4
у^4 - 26у^2 + 25 = 0
y^2 = a ; a > 0
D = 676 - 100 = 576 = 24^2
a1 = ( 26 + 24 ) : 2 = 25
a2 = ( 26 - 24 ) : 2 = 1
y^2 = 25 ==> y1 = 5 ; y2 = - 5
y^2 = 1 ==> y3 = 1 ; y4 = - 1
X = 5 / y
X1 = 5 : 5 = 1
X2 = 5 : - 5 = - 1
X3 = 5 : 1 = 5
X4 = 5 : - 1 = - 5
ответ ( 1 ; 5 ) ; ( - 1 ; - 5 ) ; ( 5 ; 1 ) ; ( - 5 ; - 1 )