X-11=+-9
x-11=9
x2-11=-9
x=20
x2=2
x+x2=22
Левая часть.
(3/(x+4))+(6x/(x^2+x-12))-(1/(x-3))=
(3(x-3)-(x+4))/((x+4)(x-3))+(6x/(x^2+x-12))=
(2x-13)/((x+4)(x-3))+(6x/((x+4)(x-3)))=
(8x-13)/((x+4)(x-3))=
(8x-13)/((x+4)(x-3)) * ((x-4)/(x-4))=
((8x-13)*(x-4))/((x^2-16)(x-3))
Поделим левую часть на правую.
[ ((8x-13)*(x-4))/((x^2-16)(x-3)) ] / ((8x-13)/(x^2-16))=
[ ((8x-13)*(x-4))/((x^2-16)(x-3)) ] * ((x^2-16)/(8x-13))=
(x-4)/(x-3)