Номер. 3
1. Х - ( х - у) = х - х+у
2. А- ( b + a) = a - b - a
3. ( m- n) + n = m - n + n
4. ( x + y) -y = x - y - y
5. 5 - ( 3 + x) = 5 - 3 - x
6. - x + ( x + 2.7) = - x + x + 2.7
7. - ( -b + 3.8) + 0.7 = - b - 3.8 - 0.7
8. 4.74 - ( 2a + 3.7 ) = 4.74 - 2a - 3.7