А+в=-1
2а+3в=-5
а=-1-в
2(-1-в)+3в=-5
в=-3
<span>а=2</span>
2.5а+4а=8.5+4.5
4.5а=13
13 делим на 4.5 и получаем ответ
<span>(4 2/3-5/9×2 4/7)+(2 1/7+1 2/3)
</span>1) 5/9 * 2 4/7 = 5/9 * 18/7 = 90/ 63 = 30/21 = 10/7 = 1 3/7
2) 4 2/3 - 1 3/7 = 14/3 - 10/7 = 98/21 - 30/21 = 68/21 = 3 5/21 = 3 5/21
3) 2 1/7 + 1 2/3 = 15/7 + 5/3 = 45/21 + 35/21 = 80/21 = 3 17/21
4) 3 5/21 + 3 17/21 = 6 22/21 = 7 1/21
Reshejiye*****************