A) y = x + 4, y = 3x
x + 4 = 3x
3x - x = 4
2x = 4
x = 2
y = 2 + 4 = 6
(2; 6) -- точка пересечения.
б) y = -2, y = 7x + 1
-2 = 7x + 1
7x = -2 - 1
7x = -3
x = -3/7
y = -2
(-3/7; -2) -- точка пересечения.
в) y = 2 - 3x, y = 5x - 4
2 - 3x = 5x - 4
5x + 3x = 2 + 4
8x = 6
x = 6/8 = 3/4
y = 2 - 3*3/4 = 2 - 9/4 = -1/4
(3/4; -1/4) -- точка пересечения.