Раскройте скобки и : 1.(х+-+2.9) 2.(a++b)+(b-c) 3.(7-m)+(m+-k) 4.(x-n)+(m--n)

1) x - 2.9
2)8 - c
3)7 + K
4)x - 5

1. (x+y)-(y-z)-(z+2.9) = x+y-y+z-z-2.9 = x-2.9
2. (a+8)-(a+b)+(b-c)  = a+8-a-b+b-c = 8-c
3. (7-m)+(m+n)-(n-k) = 7-m+m+n-n+k = 7+k
4. (x-n)+(m-5)-(m-n) = x-n+m-5-m+n = x-5