Bài 1 :
a, -5/2 : ( 3/4 - 1/2)
b ,2,8 : ( 1/5 - 3.x)= 1 2/5 ( 1 2/5 là hỗn số )
lưu ý : Câu a : Tính
Câu b ; Tìm x
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a: =3/8-1/4
=3/8-2/8
=1/8
b: =-5/9+3/5-1/9+2/5
=-2/3+1
=1/3
c: =21/7*5/25=3/5
d: =3/4+11/10:(2/5-3/2)-1/9
=-13/36
`a)3/5+(-4/9)`
`=3/5-4/9`
`=27/45-20/45`
`=7/45`
`b)3/5+2/5 . 15/8`
`=3/5 + 30/40`
`=3/5+3/4`
`=12/20+15/20`
`=27/20`
`c)7/2 . 8/13 + 8/13 . (-5/2)`
`=8/13 . (7/2 +(-5)/2)`
`=8/13 . 1`
`=8/13`
`d)-5/17 . (-9/23)+9/23 . (-22/17) + 11 9/23`
`=-5/17 . (-9/23) + 9/23 . (-1) . 22/17 + 11 + 9/23`
`=-5/17 . (-9/23) + (-9/23) . 22/17+11+9/23`
`= -9/23 ( -5/17 + 22/17)+11+9/23`
`= - 9/23 . 1+11+9/23`
`=-9/23+11+9/23`
`=(-9/23+9/23)+11`
`=0+11`
`=11`
a: =27/45-20/45=7/45
b: =3/5+30/40
=3/5+3/4
=12/20+15/20
=27/20
c: =8/13(7/2-5/2+1)=8/13*2=16/13
d: =9/23*5/17-9/23*22/17+11+9/23
=-9/23+11+9/23
=11
Mấy câu khác bạn tự tính nhé, dễ thôi. Câu 2, câu 3 giống dạng nhau. Dấu . có nghĩa là dấu nhân nhé.
Câu 2:
\(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}\)
\(=\frac{1}{2}-\frac{1}{8}\)
\(=\frac{3}{8}\)
Câu 4 b) bạn quy đồng 2 phân số cho cùng mẫu rồi tìm thôi.
a) 2/3 : 3/5 × 5/7 : 2/3
= 2/3 × 5/3 × 5/7 × 3/2
= 25/21
b) 1 1/2 × 1 1/3 × 1 1/18 × 1 1/15 × 1 1/24 × 1 1/35
= 3/2 × 4/3 × 19/18 × 16/15 × 25/24 × 36/35
= 2 × 152/35 × 15/14
= 304/35 × 15/14
= 152/7
a: =>3/5-x+13/20=5/6
=>11/10-x=5/6
=>x=11/10-5/6=4/15
b: =>x=4/9+5/9=1
c: =>3/2-2x=16/3:8/3=2
=>2x=-1/2
=>x=-1/4
d: =>x+1,5=-5/8*8/5=-1
=>x=-2,5
a) \(3\dfrac{1}{2}-1\dfrac{1}{4}\times1\dfrac{5}{6}\)
\(=\dfrac{7}{2}-\dfrac{5}{4}\times\dfrac{11}{6}\)
\(=\dfrac{7}{2}-\dfrac{55}{24}\)
\(=\dfrac{84}{24}-\dfrac{55}{24}\)
\(=\dfrac{29}{24}\)
b) \(2\dfrac{5}{6}+1\dfrac{2}{3}\div3\dfrac{3}{4}\)
\(=\dfrac{17}{6}+\dfrac{5}{3}\div\dfrac{15}{4}\)
\(=\dfrac{17}{6}+\dfrac{5}{3}\times\dfrac{4}{15}\)
\(=\dfrac{17}{6}+\dfrac{4}{9}\)
\(=\dfrac{153}{54}+\dfrac{24}{54}\)
\(=\dfrac{59}{18}\)
a) \(-\frac{5}{2}:\left(\frac{3}{4}-\frac{1}{2}\right)\)
= \(-\frac{5}{2}:\left(\frac{6}{8}-\frac{4}{8}\right)\)
= \(-\frac{5}{2}:\frac{2}{8}\)
=\(-\frac{5}{2}.\frac{8}{2}\)
=\(-\frac{40}{4}\)
=\(-10\)
b) \(2,8:\left(\frac{1}{5}-3x\right)=1\frac{2}{5}\)
=> \(\frac{14}{5}:\left(\frac{1}{5}-3x\right)=\frac{7}{5}\)
=> \(\left(\frac{1}{5}-3x\right)=\frac{14}{5}:\frac{7}{5}\)
=> \(\left(\frac{1}{5}-3x\right)=\frac{14}{5}.\frac{5}{7}\)
=> \(\frac{1}{5}-3x=2\)
=> \(3x=\frac{1}{5}-2\)
=> \(3x=-\frac{9}{5}\)
=> \(x=-\frac{9}{5}:3\)
=> \(x=-\frac{3}{5}\)
a) \(\frac{-5}{2}:\left(\frac{3}{4}-\frac{1}{2}\right)\\ =\frac{-5}{2}:\left(\frac{3}{4}-\frac{2}{4}\right)\\ =\frac{-5}{2}:\frac{1}{4}\\ =\frac{-5}{2}\cdot4=-10\)
b) \(2,8:\left(\frac{1}{5}-3x\right)=1\frac{2}{5}\\ \Rightarrow\frac{14}{5}:\left(\frac{1}{5}-3x\right)=\frac{7}{5}\\ \Rightarrow\frac{1}{5}-3x=\frac{14}{5}:\frac{7}{5}\\ \Rightarrow\frac{1}{5}-3x=\frac{14}{5}\cdot\frac{5}{7}\\ \Rightarrow\frac{1}{5}-3x=2\\ \Rightarrow3x=\frac{1}{5}-2\\ \Rightarrow3x=\frac{-9}{5}\\ \Rightarrow x=\frac{-9}{5}:3\\ \Rightarrow x=\frac{-9}{5\cdot3}=\frac{-3}{5}\)
Vậy \(x=\frac{-3}{5}\)