For each pair of real numbers a≠b,define the operationg★as(a★b)=a+b\a-b.Then the value of((1★2)★3)is( ).

For each pair of real numbers a≠b,define the operationg★as(a★b)=a+b\a-b.Then the value of((1★2)★3)is( ).
For each pair of real numbers a≠b,
define the operationg★as(a★b)=a+b\a-b.
Then the value of((1★2)★3)is( ).

For each pair of real numbers a≠b,define the operationg★as(a★b)=a+b\a-b.Then the value of((1★2)★3)is( ).
1★2=（1+2）/(1-2)=-3
-3★3=（-3+3）/(-3-3)=0

a+b\a-b代表什么？
1★2=(1+2)/(1-2)=-3
((1★2)★3)=(-3★3)=0