a) Since division by zero is undefined, we have that
![13-x\\eq0\Leftrightarrow x\\eq13](https://img.qammunity.org/2022/formulas/mathematics/college/v849d8888w0zfk6phnl2v5r7xypmed9uyy.png)
In interval notation
![D=( -\infty ,13) \cup ( 13,\infty )](https://img.qammunity.org/2022/formulas/mathematics/college/i7m8qw1ydmk4y19pfpnvj20ato7lvav9bb.png)
b) Since a square root of a negative number is undefined over the Reals, we have that
![9+x\geqslant 0\Leftrightarrow x\geqslant -9](https://img.qammunity.org/2022/formulas/mathematics/college/j3ms73jaq2m6bunstlkjkfxhfyw5fsbtfa.png)
In interval notation
![D=[-9,\infty )](https://img.qammunity.org/2022/formulas/mathematics/college/tntoakjeaj1ngp54x3cflpybb53ggzzc52.png)
c)Since division by zero is undefined, we have that
![2x+1\\eq 0\Leftrightarrow 2x\\eq -1\Leftrightarrow x\\eq -(1)/(2)](https://img.qammunity.org/2022/formulas/mathematics/college/4wopijbucvx4r1iu41xng4dgsdl5doydjl.png)
In interval notation
![D=\left( -\infty ,-(1)/(2)\right) \cup \left( -(1)/(2) ,\infty \right)](https://img.qammunity.org/2022/formulas/mathematics/college/bjzbb7wg9ia1zylmg4i4ljatnp3onwlbbe.png)
d) Since a square root of a negative number is undefined over the Reals, we have that
![4x-3\geqslant 0\Leftrightarrow 4x\geqslant 3\Leftrightarrow x\geqslant (3)/(4)](https://img.qammunity.org/2022/formulas/mathematics/college/a29vykjqnppanfcjmmr7wcj7yn9mybaakf.png)
In interval notation
![D=\left[(3)/(4) ,\infty \right)](https://img.qammunity.org/2022/formulas/mathematics/college/6nek1j7ovkb98w7dwikn86bwihgicqyrmj.png)