Помогите решить системы)

A) $\left \{ {{x^2+y^2=25} \atop {x+y=7}} \right.$

$\left \{ {{x^2+y^2=25} \atop {y=7-x}} \right.$

$x^{2} +(7-y)^2=25$
$x^{2} +49-14x+x^2=25$
$2 x^{2} -14x+24=0$
$x^{2} -7x+12=0$
$D=49-48=1$

$\left[\begin{array}{ccc}x_{1}=(7+1)/2 \\ x_{2}=(7-1)/2 \end{array}\right]$

$\left[\begin{array}{ccc} x_{1}=4 \\ x_{2}=3 \end{array}\right]$
Если $x =4$ то $y=3$
Если $x=3$ то $y=4$

б) $\left \{ {{x^2y^2-xy=12} \atop {x+y=2}} \right.$

$\left \{ {{x^2y^2-xy=12} \atop {y=2-x}} \right.$
$x^{2} (2-x)^2-x(2-x)=12$
$x^{2} (4-2x+x^2)-2x+x^2=12$