Here is the question: Convert the decimal number 73 into signed 12-bit numbers in the following representations:

(a) Sign and magnitude

(b) 1's complement

(c) 2's complement

(a) For the binary representation of 73 (and changing it to 12-bit) I got 000001001001.

(b) Getting the 1's complement, I'm complementing each bit so I'd get 111110110110.

(c) Getting the 2's complement, I'm taking the 1's complement and then adding one to the LSB and getting 111110110111.

The answer key confirms part (a) but shows the same binary number for the remaining three parts. So am I wrong and missing something obvious here or is the key wrong?