Solve the following equations using symbolic mathematics.

(a) $x^{2}+9=0$

(b) $x^{2}+5 x-8=0$

(c) $x^{3}+11 x^{2}-7 x+8=0$

(d) $x^{4}+11 x^{3}+7 x^{2}-19 x+28=0$

(e) $x^{7}-8 x^{5}+7 x^{4}+5 x^{3}-8 x+9=0$