basically it simplifies to a=a or a true statement
distribute
A.
8-1(5x+2)=-5x-6
8-5x-2=-5x-6
-5x+6=-5x-6
6=-6
false
not an identiy
B.
7z-z+10=8z-2(z-5)
6z+10=8z-2z+10
6z+10=6z+10
true
it's an identity
C.
8m-4=5m-m+8
8m-4=4m+8
minus 4m both sides
4m-4=8
add 4
4m=12
not an identity since both sides don't end up like 12=12 or m=m
D.
6y+5=6y-5
minus 6y both sides
5=-5
false
not an identiy
answer is B
