Question

найдите значение выражения x-2y,если(x;y)-решение системы 4x=y=8,xy=4

Answer 1

$left { {{4x+y=8,} atop {xy=4}} right. left { {{y=8-4x,} atop {x(8-4x)=4}} right. left { {{y=8-4x,} atop {8x-4x^2-4=0;}} right. left { {{y=8-4x,} atop {x^2-2x+1=0;}} right. left { {{y=8-4x,} atop {(x-1)^2=0;}} right. \ left { {{y=8-4x,} atop {x-1=0;}} right. left { {{y=8-4x,} atop {x=1;}} right. left { {{x=1,} atop {y=4;}} right. \ x-2y=1-2cdot4=1-8=-7.$