câu 1;
a) -13/14+3/7 b) -9/10+0,9.(1/5-1/6):20%
c) -2/9.5/19+14/19.-2/9+24 2/9
( hổn số)
câu 2;
a) x-3/4=-11/12 b) 1/3+2/3:x=2 1/3
( hổn số)
c) 1/2x+1/4x=-3/8 d) |5x-9|+2018=2019
Câu 1:
a, $\frac{-13}{14}$ + $\frac{3}{7}$
= $\frac{-13 + 6}{14}$
= $\frac{-7}{14}$
= $\frac{-1}{2}$
b, $\frac{-9}{10}$ + 0,9 . ($\frac{1}{5}$ – $\frac{1}{6}$) : 20%
= $\frac{-9}{10}$ + $\frac{9}{10}$ . ($\frac{6 – 5}{30}$) : $\frac{1}{5}$
= $\frac{-9}{10}$ + $\frac{9}{10}$ . $\frac{1}{30}$ . 5
= $\frac{-9}{10}$ + $\frac{3}{100}$ . 5
= $\frac{-9}{10}$ + $\frac{3}{20}$
= $\frac{-18 + 3}{20}$
= $\frac{-15}{20}$
= $\frac{-3}{4}$
c, $\frac{-2}{9}$ . $\frac{5}{19}$ + $\frac{14}{9}$ . $\frac{-2}{9}$ + 24$\frac{2}{9}$
= $\frac{-2}{9}$ . ($\frac{5}{19}$ + $\frac{14}{9}$) + 24$\frac{2}{9}$
= $\frac{-2}{9}$ . 1 + 24$\frac{2}{9}$
= $\frac{-2}{9}$ + 24$\frac{2}{9}$
= 24
Câu 2:
a, x – $\frac{3}{4}$ = $\frac{-11}{12}$
x = $\frac{-11}{12}$ + $\frac{3}{4}$
x = $\frac{-11 + 9}{12}$
x = $\frac{-2}{12}$
x = $\frac{-1}{6}$
b, $\frac{1}{3}$ + $\frac{2}{3}$ : x = 2$\frac{1}{3}$
$\frac{1}{3}$ + $\frac{2}{3}$ : x = $\frac{7}{3}$
$\frac{2}{3}$ : x = $\frac{7}{3}$ – $\frac{1}{3}$
$\frac{2}{3}$ : x = $\frac{6}{3}$
$\frac{2}{3}$ : x = 2
x = $\frac{2}{3}$ : 2
x = $\frac{2}{3}$ . $\frac{1}{2}$
x = $\frac{1}{3}$
c, $\frac{1}{2}$x + $\frac{1}{4}$x = $\frac{-3}{8}$
x ($\frac{1}{2}$ + $\frac{1}{4}$) = $\frac{-3}{8}$
x ($\frac{2 + 1}{4}$) = $\frac{-3}{8}$
x . $\frac{3}{4}$ = $\frac{-3}{8}$
x = $\frac{-3}{8}$ : $\frac{3}{4}$
x = $\frac{-3}{8}$ . $\frac{4}{3}$
x = $\frac{-1}{2}$
d, |5x – 9| + 2018 = 2019
|5x – 9| = 2019 – 2018
|5x – 9| = 1
⇒\(\left[ \begin{array}{l}5x – 9 = 1\\5x – 9 = -1\end{array} \right.\)
⇒\(\left[ \begin{array}{l}5x = 1 + 9 = 10\\5x = -1 + 9 = 8\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x = 10 : 5 = 2\\ x = 8 : 5 = \frac{8}{5} \end{array} \right.\)
Chúc bạn học tốt ^^
Đáp án:
Giải thích các bước giải:
a) `-13/14`+`3/7`
= `-13/14` + `6/14`
= `-7/14` = `-1/2`
b, `-9/10`+`0,9`.(`1/5`-`1/6`) : `20%`
= `-9/10 + 9/10 . ( 6/ 30 – 5/ 30 ) : 1/5`
= `-9/ 10 + 9/ 10 . 1/ 30 : 1/5`
= `-9 / 10 + 9 / 300 : 1/5`
= `-9/ 10 + 45/ 300`
= `-27/ 300 + 45/ 300`
= `-18/300 = -3/ 50`
c) `-2/9.5/19+14/19.-2/9+24 2/9`
= `-2/9 . 5/19 + 14/ 19 . -2/9 + 218/9`
= `-10/ 171 + -28 / 171 + 4142 / 171`
= `-38/171 + 4142/ 171`
= `4104/ 171`
d, x`-3/4=-11/12`
x `- 9/12 = -11/12`
x = `-11/12 + 9/12`
x = `-2/12 = -1/6`
e, `1/3+2/3` : x = `2 1/3`
`1/3+2/3 :` x = `7/3`
`2/3 :` x = `7/3 – 1/3`
`2/3 :` x = `2`
x = `2 . 2/3`
x = `4/3`
g, 1/2x+1/4x=-3/8
x . `( 1/4 + 1/2 ) = -3/8`
x . `3/4 = -3/8`
x = `-3/ 8 : 3/4`
x = -`1/2`
h) `|5x-9|+2018=2019`
`|5x-9| = 2019 – 2018`
`|5x-9| = 1`
Ta có `2` TH :
TH`1` : `|5x-9| = 1`
`5x = 1 + 9`
`5x = 10`
`x = 10 : 2`
`x = 5`
TH`2` ; `|5x-9| = – 1`
`5x = – 1 + 9`
`5x = 8`
`x = 8 : 5`
`x = 8/5`
Vậy x = `5` hoặc `8/5`