Tìm x:
`a, 2|x + 7| = -3/4 + 5`
`-> 2|x + 7| = -3/4 + 20/4`
`-> 2|x + 7| = 17/4`
`-> |x + 7| = 17/4 : 2`
`-> |x + 7| = 17/4 . 1/2`
`-> |x + 7| = 17/8`
`->` \(\left[ \begin{array}{l}x + 7 = \frac{17}{8}\\x + 7 = \frac{-17}{8}\end{array} \right.\)
`->` \(\left[ \begin{array}{l}x = \frac{17}{8} - 7 = \frac{17}{8} - \frac{56}{8} = \frac{-39}{8}\\x = \frac{-17}{8} - 7 = \frac{-17}{8} - \frac{56}{8} = \frac{-73}{8}\end{array} \right.\)
Vậy `x ∈ { -39/8 ; -73/8 }`
`b, (2x + 3)^3 = -8/27`
`-> (2x + 3)^3 = ((-2)/3)^3`
`-> 2x + 3 = -2/3`
`-> 2x = -2/3 - 3`
`-> 2x = -2/3 - 9/3`
`-> 2x = -11/3`
`-> x = -11/3 : 2`
`-> x = -11/3 . 1/2`
`-> x = -11/6`
Vậy `x = -11/6`
Thực hiện phép tính:
`14/25 + 6/18 + 11/25 - 20/15 - 7/5`
`= (14/25 + 11/25) + 6/18 - 20/15 - 7/5`
`= 1 + 1/3 - 4/3 - 7/5`
`= 1 + (-1) - 7/5`
`= 0 - 7/5`
`= -7/5`
