Question

Числа х и у таковы что х-2у=2 ху=4 найти х+2у

Answer 1

X - 2у = 2
ху = 4

Решение :
x = 2у + 2
у ( 2у + 2 ) = 4
2у^2 + 2у - 4 = 0
2 ( у^2 + у - 2 ) = 0
D = 1 + 8 = 9 = 3^2
y1 = ( - 1 + 3 ) : 2 = 1
y2 = ( - 1 - 3 ) : 2 = - 2
x1 = 2•1 + 2 = 4
x2 = 2•( - 2 ) + 2 = - 2
( 4 ; 1 ) ; ( - 2 ; - 2 )

x + 2y
1) 4 + 2 = 6
2) - 2 + 2•( - 2 ) = - 2 - 4 = - 6

ответ 6 ; ( - 6 ).

Answer 2

$x - 2y = 2 \\ xy = 4$
$x = 2y + 2 \\ xy = 4$
$2 {y}^{2} + 2y = 4 \\ {y}^{2} + y = 2$
${y}^{2} = 1 = y = 1 \\ y = - 2$
$x - 2y = 2 \\ x = 2y + 2 \\ x = 2 \times 1 + 2 = 4 \\ x = (2 \times - 2 )+ 2 = - 2$

ответ (х,у)=(4,1)
(х,у) = (-2,-2)
х+2у = 6,-6