Найди недопустимые значения переменной

\(\dfrac{x^2-1}{x+4}\) ; \(x \kern{0.27em}{=}\mathllap{/\,}\kern{0.27em} \) [0|4|-4]

\(\dfrac{3}{2y+8}\) ; \(y \kern{0.27em}{=}\mathllap{/\,}\kern{0.27em} \) [-4|4|8]

\(\dfrac{a+1}{a+6}\) ; \(a \kern{0.27em}{=}\mathllap{/\,}\kern{0.27em} \) [-1|6|-6]