Решите систему уравнений: а) {3x-y=4, {2x+3y=21 б) {x-y=3, {-x-4y=7 в) {4x+3y=10,...

$\left \{ {{3x - y=4} \atop {3x + 3y=21}} \right.$
1) y=3x-4
2)2x + 3(3x - 4)=21
2x + 9x -12 = 21
11x = 33
x = 3
3) y = 3 · 3 - 4
y = 5 (3;5)

$\left \{ {{x - y=2} \atop {- x - 4y=7}} \right.$
1)x=3 + y
2) - (3 + y) -4y = 7
-3 -y -4y = 7
-5y= 10
y= -2
3) x= 3 - 2
x = 1 (1;-2)

$\left \{ {{4x + 3y=10} \atop {x -2y = -3}} \right.$
1) x = 2y - 3
2) 4(2y - 3) + 3y = 10
8y -12 +3y = 10
11y = 22
y = 2
3) x = 2 ·2 -3
x=1 (1;2)