ц-целые
9ц5/28-(7ц1/7-х)=2ц4/21,приведем к общему знаменателю.Так как целые части можно и так вичислять,то в неправильные дроби не будем переводить.Общий знаменатель 84
9ц15/84-(7ц12/84-х)=2ц16/84,откроем скобки
9ц15/84-7ц12/84+х=2ц16/84
х=2ц16/84+7ц12/84-9ц15/84
х=9ц28/84-9ц15/84
х=13/84
Проверка
9ц15/84-7ц12/84+13/84=2ц16/84
2ц3/84+13/84=2ц16/84
2ц16/84=2ц16/84
1]240:3=80[км]-за 1 час
2]80×5=400[км]-за 5 часов
Ответ:400 км за 5 часов
![f( z_{0})=(1+2i)+ \frac{2}{(1+2i)(1+2i-1)}=1+2i+ \frac{2}{(1+2i)2i}=1+2i+ \frac{1}{i+2 i^{2} }=1+2i+ \frac{1}{i-2}=1+2i- \frac{1}{2-i}= \frac{(1+2i)(2-i)-1}{2-i}= \frac{2+4i-i- 2i^{2}-1}{2-i}= \frac{3+3i}{2-i}= \frac{3(1+i)(2+i)}{(2-i)(2+i)}= \frac{3(2+2i+i+ i^{2})}{4- i^{2} } = \frac{3(1+3i)}{4+1}= \frac{3+9i}{5}](https://tex.z-dn.net/?f=f%28+z_%7B0%7D%29%3D%281%2B2i%29%2B+%5Cfrac%7B2%7D%7B%281%2B2i%29%281%2B2i-1%29%7D%3D1%2B2i%2B+%5Cfrac%7B2%7D%7B%281%2B2i%292i%7D%3D1%2B2i%2B+%5Cfrac%7B1%7D%7Bi%2B2+i%5E%7B2%7D+%7D%3D1%2B2i%2B+%5Cfrac%7B1%7D%7Bi-2%7D%3D1%2B2i-+%5Cfrac%7B1%7D%7B2-i%7D%3D+%5Cfrac%7B%281%2B2i%29%282-i%29-1%7D%7B2-i%7D%3D+%5Cfrac%7B2%2B4i-i-+2i%5E%7B2%7D-1%7D%7B2-i%7D%3D+%5Cfrac%7B3%2B3i%7D%7B2-i%7D%3D+%5Cfrac%7B3%281%2Bi%29%282%2Bi%29%7D%7B%282-i%29%282%2Bi%29%7D%3D+%5Cfrac%7B3%282%2B2i%2Bi%2B+i%5E%7B2%7D%29%7D%7B4-+i%5E%7B2%7D+%7D+%3D+%5Cfrac%7B3%281%2B3i%29%7D%7B4%2B1%7D%3D+%5Cfrac%7B3%2B9i%7D%7B5%7D++++++++++++)
по определению мнимой единицы:
![i^{2}=-1](https://tex.z-dn.net/?f=+i%5E%7B2%7D%3D-1+)