Question

решить систему уравнений (x+y=6)(xy=-7)

Answer 1

$left { {{x+y=6} atop {xy=-7}} right. Longleftrightarrow left { {{x=6-y} atop {(6-y)y=-7}} right. Longleftrightarrow left { {{x=6-y} atop {6y-y^2=-7}} right. Longleftrightarrow left { {{x=6-y} atop {6y-y^2+7=0}} right. Longleftrightarrow \ Longleftrightarrow left { {{x=6-y} atop {-y^2+6y+7=0}} right. Longleftrightarrow left { {{x=6-y} atop {y=-1}} right. Longleftrightarrow left { {{x=6-(-1)} atop {y=-1}} right. Longleftrightarrow$
$Longleftrightarrow boxed{ left { {{x=7} atop {y=-1}} right.}$