-17+(х+3)=20
-17+х+3=20
х=20+17-3
х=34
.........................
5-(2-х)=3,5
5-2+х=3,5
х=3,5-5+2
х=0,5
.........................
3,3-(х-5,2)=90
3,3-х+5,2=90
-х=90-3,3-5,2
-х=81,5
х=-81,5
.........................
(m+2)-(4+m)=m+2-4-m=-2
.........................
m-(a+m)=m-a-m=-a
.........................
а-(а+b)=a-a-b=-b
.........................
а-(а-b)=a-a+b=b
.........................
-n+(x+n)=-n+x+n=x
.........................
(a+b)+(р-b)=a+b+p-b=a+p