`5,``x + 2x + 3x + 4x + ... + 100x = -213`
`⇒x( 1 + 2 + 3 + 4 + ... + 100 ) = -213`
`⇒x. 5050 = -213`
`⇒x = \frac{-213}{5050}`
`6,` `3(x - 2)+ 2(x-1) = 10`
`⇒ 3x - 6 + 2x - 2 = 10`
`⇒ 3x + 2x = 10 + 2 + 6 = 18`
`⇒ 5x = 18`
`⇒ x = \frac{18}{5}`
` XIN` `HAY` `NHẤT`