Đáp án:
`↓↓↓`
Giải thích các bước giải:
`a) (x+5)/65+(x+10)/60=(x+15)/55+(x+20)/50`
`=> (x+5)/65 + 1 + (x+10)/60 + 1 = (x+15)/55 + 1 +(x+20)/50 +1`
`=> (x+70)/65 + (x+70)/60 = (x+70)/55 + (x+70)/50`
`=> (x+70)/65 + (x+70)/60 - (x+70)/55 - (x+70)/50 = 0`
`=> (x+70) . (1/65+1/60+1/55+1/50)=0`
Mà `1/65+1/60+1/55+1/50>0`
`=> x+70=0`
`=> x=-70`
`b) (x+91)/81 + (x+92)/82 + (x+93)/83=3`
`=> (x+91)/81 + (x+92)/82 + (x+93)/83 - 3=0`
`=> (x+91)/81 -1 + (x+92)/82 -1 + (x+93)/83 -1 =0`
`=> (x+10)/81 + (x+10)/82 + (x+10)/83=0`
`=> (x+10) . (1/81 + 1/82 + 1/83)=0`
Mà `1/81 + 1/82 + 1/83>0`
`=> x+10=0`
`=> x=-10`
