negative
Be Certain of this: it is by happy coincidence that the high order bit of a two's comp. integer is 0 for positive and 1 for negative. But, to create the two's comp. repn of the negative of a number you must "reflect, add one". Changing the sign bit by itself will not work.
To convert N bits of two's complement representation into decimal representation:
The number repd by 1001 is negative (since the "sign bit" is one), so complement:
1001 → 0110 + 1 → 0111
Convert the result to decimal: