Please show work so I can see how to do it.

Answer:
a. D = R \ {13}
b. D = [-9;+∞)
D = R \ { [tex]\frac{-1}{2}[/tex] }
Step-by-step explanation:
a. 13 - x ≠ 0
x ≠ 13
D = R \ {13}
b. 9 + x ≥ 0
x ≥ -9
D = [-9;+∞)
c. 2x + 1 ≠ 0
x ≠ [tex]\frac{-1}{2}[/tex]
D = R \ { [tex]\frac{-1}{2}[/tex] }