Bài 1:
a, `(-12) . 3 - (-4) - 7 . 0 + 1`
`= -36 + 4 - 0 + 1`
`= -31`
b, `(-21) . 85 - ( -21 ) . 15 + 100`
`= (-21) . ( 85 + 15 ) + 100`
`= ( -21 ) . 100 + 100`
`= 100 . ( 1 - 21 )`
`= 100 . ( -20 )`
`= -2000`
c, `-2/5 + 7/5 . 10/3`
`= -2/5 + 14/3`
`= -6/15 + 70/15`
`= 64/15`
d, `1\frac{7}{20} : 2,7 + 0,4 . 5/3 - 1/2`
`= 27/20 . 10/27 + 2/5 . 5/3 - 1/2`
`= 1/2 + 2/3 - 1/2`
`= 2/3`
Bài 2:
a, `7x + 4 = ( -3 ) . 8`
`7x + 4 = -24`
`7x = -28`
`x = -4`
Vậy `x=-4`
b, `-3/4x = 1/6`
`x = 1/6 . (-4)/3`
`x = -2/9`
Vậy `x=-2/9`
c, `1/2 - ( x - 2/3 ) = 5/6`
`x - 2/3 = 1/2 - 5/6`
`x - 2/3 = -1/3`
`x = 1/3`
Vậy `x=1/3`
d, `4/5 . | x + 2 | = 8/3`
`| x + 2 | = 8/3 . 5/4`
`| x + 2 | = 10/3`
`=>` \(\left[ \begin{array}{l}x+2=\frac{10}{3}\\x+2=-\frac{10}{3}\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=\frac{4}{3}\\x=\frac{-16}{3}\end{array} \right.\)
Vậy \(\left[ \begin{array}{l}x=\frac{4}{3}\\x=\frac{-16}{3}\end{array} \right.\)
