Đáp án:
`Azzuri#`
Bài 1:
`8x - 20/11.13 - 20/13.15 - 20/15.17 -...-20/53.55 = 3/11`
`=> 8x -( 20/11.13 + 20/13.15 +...+ 20/53.55) = 3/11`
`=> 8x- 10(2/11.13 + 2/13.15 +...+ 2/53.55) = 3/11`
`=> 8x - 10( 1/11 -1/13 + 1/13 -1/15 +...+1/53 - 1/55) = 3/11`
`=> 8x- 10( 1/11 - 1/55) = 3/11`
`=> 8x - 10. 4/55 = 3/11`
`=> 8x - 8/11=3/11`
`=> 8x = 3/11 + 8/11`
`=> 8x=11/11=1`
`=> x= 1/8`
Bài 2:
`1/2.4 + 1/4.6 +...+ 1/((2x-2).2x) =1/8`
`=> 2 ( 1/2.4 + 1/4.6 +... + 1/((2x-2).2x) ) = 1/8 .2`
`=> 2/2.4 + 2/4.6 +...+ 2/[(2x-2)(2x)] = 1/4`
`=> 1/2 - 1/4 + 1/4 - 1/6+...+ 1/(2x-2) - 1/(2x) = 1/4`
`=> 1/2 - 1/(2x) =1/4`
`=> 1/(2x) = 1/2 - 1/4`
`=> 1/(2 x) =1/4`
`=> 2x =4`
`=>x=2`
Giải thích các bước giải:
