Giải thích các bước giải:
`a)`
`(1/1.3 +1/3.5 + 1/5.7 +...+1/97.99) . 2x = 2/3`
`(2/1.3+2/3.5+2/5.7+...+2/97.99):2.2x=2/3`
`(1-1/3+1/3-1/5+1/5-1/7+...+1/97-1/99).x=2/3`
`(1-1/99).x=2/3`
`(99/99-1/99).x=2/3`
`98/99.x=2/3`
`x=2/3:98/99`
`x=2/3. 99/98`
`x=33/49`
Vậy `x=33/49`
`b)`
`(1/[1.2.3] + 1/[2.3.4 ]+ 1/[3.4.5] +...+ 1/[98.99.100]) . x = -3`
`(2/[1.2.3] + 2/[2.3.4 ]+...+ 2/[98.99.100]) :2. x = -3`
`(1/1.2-1/2.3+1/2.3-1/3.4...+1/98.99-1/99.100):2.x=-3`
`(1/1.2+1/99.100). 1/2.x=-3`
`1/2.2-1/[99.100.2].x=-3`
`1/4-1/19800.x=-3`
`4950/19800-1/19800.x=-3`
`4949/19800.x=-3`
`x=-3:4949/19800`
`x=-3. 19800/4949`
`x=-59400/4949`
Vậy `x=-59400/4949`