Răspuns:
{-5}
Explicație pas cu pas:
[tex]x\neq 0~si~x\neq 3.\\\dfrac{1}{x}+\dfrac{1}{x-3}=\dfrac{12}{x(x-3)},~\dfrac{x-3}{x(x-3)}+\dfrac{x(x+1)}{x(x-3)}=\dfrac{12}{x(x-3)},~ ~\\\dfrac{x-3+x^{2}+x}{x(x-3)}=\dfrac{12}{x(x-3)},~deci~x^{2}+2x-3=12,~x^{2}+2x-3-12=0\\x^{2}+2x-15=0, deta=2^{2}-4*1*(-15)=64>0, ~deci~x_{1}=\dfrac{-2-8}{2}=-5\\ x_{2}=\dfrac{-2+8}{2}=3.~Dar~x\neq 3,~deci~ecuatia~are~o~singura~solutie\\[/tex]
S={-5}