a/ \(\dfrac{x}{2(x-3)}+\dfrac{x}{2x+2}=\dfrac{2x}{(x+1)(x-3)}(x\ne -1;3)\\↔\dfrac{x(x+1)}{2(x-3)(x+1)}+\dfrac{x(x-3)}{2(x+1)(x-3)}=\dfrac{4x}{2(x+1)(x-3)}\\→x^2+x+x^2-3x=4x\\↔2x^2-2x-4x=0\\↔2x^2-6x=0\\↔x(2x-6)=0\\↔x=0\quad or\quad 2x-6=0\\↔x=0(TM)\quad or\quad x=3(KTM)\\\text{Vậy pt có tập nghiệm}\,\,S=\{0\}\)
b/ \(\dfrac{x-12}{77}+\dfrac{x-11}{78}=\dfrac{x-74}{15}+\dfrac{x-73}{16}\\↔(\dfrac{x-12}{77}-1)+(\dfrac{x-11}{78}-1)=(\dfrac{x-74}{15}-1)+(\dfrac{x-73}{16}-1)\\↔\dfrac{x-99}{77}+\dfrac{x-99}{78}-\dfrac{x-99}{15}-\dfrac{x-99}{16}=0\\↔(x-99)(\dfrac{1}{77}+\dfrac{1}{78}-\dfrac{1}{15}-\dfrac{1}{16})=0\\↔x-99=0(vì\,\,\dfrac{1}{77}+\dfrac{1}{78}-\dfrac{1}{15}-\dfrac{1}{16}\ne 0)\\↔x=99\\\text{vậy pt có tập nghiệm}\,\, S=\{99\}\)
