Решите в каждом номере 2,3 - системы (а), (б) Пожалуйста

2)a) $\left \{ {{x-y=-2} \atop {x-2y=4}} \right. \left \{ {{x=y-2} \atop {y-2-2y=4}} \right. \left \{ {{x=y-2} \atop {-y=4+2}} \right. \left \{ {{x=-6-2=-8} \atop {y=-6}} \right.$

2)б) $\left \{ {{2x-3y=11} \atop {4x+5y=-11}} \right. \left \{ {{x= \frac{11+3y}{2} } \atop {4*\frac{11+3y}{2} +5y=-11}} \right. \left \{ {{x=\frac{11+3y}{2} } \atop {22+6y+5y=-11}} \right. \left \{ {{x=\frac{11+3y}{2} } \atop {11y=-11-22}} \right.$ $\left \{ {{x=\frac{11+3(-3)}{2} } \atop {y=-3}} \right. \left \{ {{x=1} \atop {y=-3}} \right.$

3)a) $\left \{ {{4x-y=-2} \atop {x+y=3}} \right. (+ )$ ⇒4x-y+x+y=-2+3 ⇒
5x=1 ⇒ x=1/5 ⇒ y=3-x=3-1/5=14/5

б) $\left \{ {{x+y=4} \atop {3x-5y=20}} \right.$
5(x+y)+3x-5y=5*4+20 ⇒ 5x+5y+3x-5y=20+20⇒ 8x=40 ⇒ x=5
y=4-x=4-5=-1