Question

(x+1)+(x+2)+(x+3)+...(x+14)+(x+15)=135

Answer 1

`(x + 1) + (x + 2)+(x + 3) + ...+(x + 14) + (x  + 15)=135`

`=> (x + x + x + ... + x (15` chữ `x) +[(15-1):1+1]=135`

`=> 15x + [(15+1)xx15:2] = 135`

`=> 15x+120=135`

`=> 15x= 135-120`

`=> 15x=15`

`=> x = 15:15`

`=> x=1`

Answer 2

`(x+1)+(x+2)+(x+3)+.....+(x+15)=135`

`x+1+x+2+x+3+......+x+15=135`

`=>(x+x+.....+x)+(1+2+3+......+15)=135`

`=>1+2+3+.....+15`

Số hạng:

`(15-1)/1+1= 15(số)`

Tổng:

`(15+1)xx15:2=120`

`=>15x+120=135`

`15x=135-120`

`15x=15`

`x=15:15`

`x=1`