(x+4/10 + 1) + (x+3/11 +1) = (x+2/12 +1) + (x+1/13 +1)
(x+4/10 + 1) + (x+3/11 +1) - (x+2/12 +1) - (x+1/13 +1)=0
x+14/10 + x+14/11 - x+14/12 - x+14/13=0
x+14.(1/10 + 1/11 - 1/12 - 1/13)=0
1/10>1/11>1/12>1/13 nên dễ thấy 1/10+ 1/11 - 1/12 - 1/13 khác 0
=> x+14=0
x= -14