<span>3y - 2x = 10 /*7
7x + </span>5y<span> = 27 /*2
21y - 14x = 70
10y + 14x = 54
============= +
31y = 124
y = 4
x = (27 - 5y)/7 = (27 - 20)/7 = 7/7 = 1
Ответ
(1; 4)
</span>
Решение
<span>cos (π-a) × cos (2π-a)+cos ²a = - cosa * (- cosa) + cos</span>²a = cos²a + cos²a = = 2cos²a