`(3x)/(2 × 5) + (3x)/(5 × 8) + (3x)/(8 × 11) + (3x)/(11 × 14) = 1/21`
`⇔ (3x)/10 + (3x)/40 + (3x)/(8 × 11) + (3x)/(11 × 14) = 1/21`
`⇔ 1/8 × 3x + (3x)/(8 × 11) + (3x)/(11 × 14) = 1/21`
`⇔ 1/8 × 3x + (3x)/88 + (3x)/(11 × 14) = 1/21`
`⇔ 3/22 × 3x + (3x)/(11 × 14) = 1/21`
`⇔ 3/22 × 3x + (3x)/154 = 1/21`
`⇔ 1/7 × 3x = 1/21`
`⇔ 3/7x = 1/21`
`x = 1/21 × (7/3)`
`x = 7/63`
`x = 1/9`
Cho mình xin hay nhất nha bạn!!!!!
@Drew Mclntyre
