Đáp án:
2/(x-14)-5/(x-13)=2/(x-9)-5/(x-11)
=> 2(x-13)(x-9)(x-11)-5(x-14)(x-9)(x-11)=2(x-14)(x-13)(x-11)
=> (2x-26)(x-9)(x-11)-(5x-70)(x-9)(x-11)=(2x-28)(x-13)(x-11)
=> (2x²-18x-26x+234)(x-11)-(5x²-45x-70x+630)(x-11)=(2x²-26x-28x+364)(x-11)
=> (2x²-44x+234)(x-11)-(5x²-115x+630)(x-11)=(2x²-54x+364)(x-11)
=> 2x³-22x²-44x²+484x+234x-2574-(5x³-55x²-115x²+1265x+630x-6930)=(2x³-22x²-54x²+594x+364x-4004)
=> 2x³-22x²-44x²+484x+234x-2574-5x³+55x²+115x²-1265x-630x+6930-2x³+22x²+54x²-594x -364x+4004
=> -5x³+158x²-2135x+8360=0
=> x=6,2 và x=12,7 và x=12,7 (mode 5->4)
Vậy S={6,2;12,7}
