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\(a,\dfrac{6}{5}=\dfrac{18}{x}\\ \Rightarrow x=18:\dfrac{6}{5}\\ \Rightarrow x=15\\ b,\dfrac{3}{4}=\dfrac{-21}{x}\\ \Rightarrow x=-21:\dfrac{3}{4}\\ \Rightarrow x=-28\\ c,\dfrac{2}{-7}=\dfrac{18}{x}\\ \Rightarrow x=18:\dfrac{2}{-7}\\ \Rightarrow x=-63\\ d,\dfrac{-5}{2}=\dfrac{10}{-x}\\ \Rightarrow x=-10:\dfrac{-5}{2}\\ \Rightarrow x=4\)
\(a,\dfrac{6}{5}=\dfrac{18}{x}\Rightarrow6.x=5.18=90\\ \Rightarrow6.x=90\\ \Rightarrow x=15\\ b,\dfrac{3}{4}=\dfrac{-21}{x}\Rightarrow3.x=4.21=84\\ \Rightarrow x=28\)
\(a,\dfrac{x}{7}=\dfrac{6}{21}\Rightarrow x.21=7.6=42\\ \Rightarrow x=2\\ b,\dfrac{1}{2}=\dfrac{x}{12}\Rightarrow1.12=2.x=12\\ \Rightarrow x=6\\ c,\dfrac{-7}{6}=\dfrac{x}{12}\Rightarrow-7.12=6.x=-84\\ \Rightarrow x=-14\)
2:
a: =>x-1/5=2/15
=>x=2/15+3/15=5/15=1/3
b: =>x+7/12=-5/6-2/6=-7/6
=>x=-14/12-7/12=-21/12=-7/4
c: =>x+2/3=-10/3
=>x=-4
d: =>1/4:x=-11/4
=>x=-1/4:11/4=-1/11
e: =>8:x=1,6
=>x=5
a 25 phần 41
b 9
c 1 phần 12
d 12
e 14 phần 15
f 24 phần 7
Bài 1 :Bỏ dấu ngoặc
2007-(7-3+4)
= 2007 -7+3-4
= 1999
6+[(-5) + 4 - 1 ]
= 6-5+4-1
=4
5-[(-6+8-2]
= 5+6-8+2
=5
-10+(7-3+1)
= -10 +7-3+1
= -5
Bài 3 Tìm x
\(\dfrac{1}{3} = \dfrac{x}{6}\)
\(<=> x= \dfrac{1.6}{3}\)
\(<=> x=2\)
a) \(\frac{2}{3x}=\frac{5}{2}\Leftrightarrow3x=\frac{4}{5}\Rightarrow x=\frac{4}{15}\)
b) \(\frac{x-3}{4}=\frac{1}{2}\Rightarrow x-3=2\Rightarrow x=5\)
c) \(\frac{5}{24+x}=\frac{7}{12}\Rightarrow24+x=\frac{60}{7}\Rightarrow x=\frac{-108}{7}\)
d) \(-6x=18\Rightarrow x=-3\)