<span>cos17cos73=0.5(cos90+cos56)</span>
<span><span>sin13cos21=0.5(sin34-sin8)</span></span>
<span><span><span>cos4cos86=0.5(cos90+cos82)</span></span></span>
<span><span><span>cos90=0</span></span></span>
<span><span><span>cos56=cos(90-34)=sin34</span></span></span>
<span><span><span>cos82=cos(90-8)=sin8</span></span></span>
<span><span><span><span>cos17cos73-sin13cos21-cos4cos86=0.5(sin34-sin34+sin8-sin8)=0</span></span></span></span>
1 и 4 неверны как я поняла) 1 точно неверно
Умножим второе уравнение на (-1)
Получим:
![\left \{ {{3x-2y=64} \atop {-3x-7y=8}} \right.](https://tex.z-dn.net/?f=+%5Cleft+%5C%7B+%7B%7B3x-2y%3D64%7D+%5Catop+%7B-3x-7y%3D8%7D%7D+%5Cright.+)
Сложим оба уравнения:
![-9y=72](https://tex.z-dn.net/?f=-9y%3D72)
![y=-8](https://tex.z-dn.net/?f=y%3D-8)
<em><u>Ответ: 6;-8</u></em>