a)
y=\frac{3x-2}{x+6}
x+6\ne0
x\ne-6
x\in R||-6
b)
y=\frac{5}{(x-3)(x+12)}
x-3\ne0\Rightarrow x\ne3
x+12\ne0\Rightarrow x\ne-12
x\in R||3,||-12
c)
y=\frac{2x+1}{x^2-1}
x^2-1\ne0\Rightarrow x\ne 1 i x\ne-1
x\in R||1, ||-1
d)
y=\frac{3x}{x^2(x+5)}
x^2\ne0\Rightarrow x\ne 0
x+5\ne0\Rightarrow x\ne -5
x\in R||0, ||-5