here, 2 in binary(8 bit) is 00000010 and its 1's complement is 11111101,
subtract 1 from that 1's complement we get 11111101-1 = 11111100,
here the sign is - as 8th character (from R to L) is 1
find 1's complement of that no. i.e. 00000011 = 3
and the sign is negative that's why we get -3 here.