7)
2x - y = 5
3x + 2y = 4
y = 2x - 5
3x + 2*(2x - 5) = 4
y = 2x - 5
3x + 4x - 10 = 4
y = 2x - 5
7x = 14
x = 2
y = 2x - 5
x = 2
y = 4 - 5 = -1
Ответ: D) (2; -1)
8) S7 = (2a1 + d*(n - 1))/2 * n = (2a1 + 6d)/2 * 7 = (a1 + 3d)*7
a1 = 10
d = a2 - a1 = 5 - 10 = -5
S7 = (a1 + 3d)*7 = (10 + 3*(-5))*7 = -5*7 = -35
Ответ: C)