`(2x + 1)/(2x) + (6x+1)/(6x) + ....+ (30x+1)/(30x) = 6`
`=> (2x)/(2x) + 1/(2x) + (6x)/(6x) + 1/(6x) + ....+ (30x)/(30x) + 1/(30x) = 6`
`=> 1+ 1/(2x) + 1 + 1/(6x) + ....+ 1 + 1/(30x) = 6`
`=> 5 + 1/(2x) + 1/(6x) + ....+ 1/(30x) = 6`
`=> 1/(2x) + 1/(6x) + ....+ 1/(30x) = 1`
`=> 1/(2) xx 1/x + 1/(6) xx 1/x + ....+ 1/(30) xx 1/x = 1`
`=> 1/x xx (1/2 + 1/6 + ....+ 1/30) = 1`
`=> 1/x xx (1/(1xx2) + 1/(2xx3) + ....+ 1/(5xx6)) = 1`
`=> 1/x xx (1 - 1/2 + 1/2 - 1/3 +....+ 1/5 - 1/6) = 1`
`=> 1/x xx (1 - 1/6) = 1`
`=> 1/x xx 5/6 = 1`
`=> 1/x = 6/5`
`=> x = 5/6`
nên `1/x = 1 : 5/6 = 6/5`
=(1+1/2x)+(1+1/6x)+...+(1+1/30x)=6
=(1+1+1+1+1)+(1/2x+...+1/30x)=6
=5+1/2x+...+1/30x=6
=1/2x+...+1/30x = 1
= 1/x.(1/2+1/6+...+1/30)=1
=1/x.(1-1/2+1/2-...+1/5-1/6)=1
=1/x.(1-1/6) =1
=1/x. 5/6 = 1
=> 1/x = 1: (5/6) = 6/5
=> x = 1: (6/5) = 5/6
