Method 1: $\color{blue}{-(105.75) = -106 + 0.25}$
Convert both of these to $2's$ complement representation and add them.
$10010110 = -128 + 16 + 6 = -106 $ and $0.25 = 0.01$ So, combining these two, we get $\color{red}{-(105.75) = 10010110.01}$
Method 2: This is the method we generally follow to find $2's$ complement representation of any negative number.
- Firstly find binary representation of $+ve$ number i.e., $(105.75)_{10} = 01101001.11$
- Take $1's$ complement of the number, now we get $10010110.00$
- Now, add $1$ to LSB, So we add $0.01$ here to above number.
- $10010110.00 + 0.01 = 10010110.01 $
PS:) I followed method $1$, when I gave this test.