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\(a.\dfrac{6}{5}=\dfrac{18}{x}\Rightarrow x=\dfrac{18\cdot5}{6}=15\\ \text{Vậy}\text{ }x=15.\)
\(b.\dfrac{3}{4}=\dfrac{-21}{x}\Rightarrow x=\dfrac{-21\cdot4}{3}=28\\ \text{ }\text{ }\text{ }\text{ }\text{Vậy }x=28.\)
\(c.\dfrac{x}{4}=\dfrac{21}{28}\Rightarrow x=\dfrac{21\cdot4}{28}=3\\ \text{Vậy }x=3.\)
\(d.\dfrac{-8}{2x}=\dfrac{3}{-9}\Rightarrow x=\dfrac{-8\cdot\left(-9\right)}{3}:2=12\\ \text{Vậy }x=12.\)
\(e.\dfrac{-4}{11}=\dfrac{x}{22}=\dfrac{40}{z}\\ \Rightarrow x=\dfrac{-4\cdot22}{11}=-8\\ \Rightarrow z=\dfrac{22\cdot40}{-8}=-110\\ \text{Vậy }x=-8;z=-110.\)
\(f.\dfrac{-3}{4}=\dfrac{x}{20}=\dfrac{21}{y}\\ \Rightarrow x=\dfrac{-3\cdot20}{4}=-15\\ \Rightarrow y=\dfrac{21\cdot20}{-15}=-28\\ \text{Vậy }x=-15;y=-28.\)
\(g.\dfrac{-4}{8}=\dfrac{x}{-10}=\dfrac{-7}{y}=\dfrac{z}{-24}\\ \Rightarrow x=\dfrac{-4\cdot\left(-10\right)}{8}=5\\ \Rightarrow y=\dfrac{-7\cdot\left(-10\right)}{5}=14\\ \Rightarrow z=\dfrac{-7\cdot\left(-24\right)}{14}=12\\ \text{Vậy }x=5;y=14;z=12.\)
\(h.\dfrac{x}{4}=\dfrac{9}{x}\\ \Rightarrow x\cdot x=9\cdot4\\ \Rightarrow x\cdot x=36\\ \Rightarrow x\cdot x=6\cdot6\\ \text{Vậy }\text{cả hai }x=6.\)
a: =30-22=8
b: =10*(23+17)=10*40=400
c: =21*3-7*(-14)
=63+98=161
d: =-20-[10*10*5^2+16]
=-20-100*25-16
=-36-2500
=-2536
1/13.58.4+32.26.2+52.10
=52.58+52.32+52.10
=52(58+32+10)=52.100=5200
2/15.37.4+120.21+21.5.12
=60.37+120.21+60.21
=60(37+2.21+21)=60.100=6000
x/5=2/3:16/21 b)x/10=4/5.3/4 NHỚ K NHÉ MỌI NGƯỜI
x/5=2/3.21/16 x/10=3/5
x/5=7/8 =>x=3.10/5
=>x=5.8/7 =>x=6
=>x=40/7
\(\frac{2}{3}:\frac{x}{5}=\frac{16}{21}\)
\(\Rightarrow\frac{x}{5}=\frac{2}{3}:\frac{16}{21}\)
\(\Rightarrow\frac{x}{5}=\frac{2}{3}.\frac{21}{16}\)
\(\Rightarrow\frac{x}{5}=\frac{7}{8}\)
\(\Rightarrow x=\frac{7.5}{8}\)
\(\Rightarrow x=\frac{35}{8}\)
Vậy \(x=\frac{35}{8}\)
b) \(\frac{x}{10}:\frac{3}{4}=\frac{4}{5}\)
\(\Rightarrow\frac{x}{10}=\frac{4}{5}.\frac{3}{4}\)
\(\Rightarrow\frac{x}{10}=\frac{3}{5}\)
\(\Rightarrow x=\frac{3.10}{5}\)
\(\Rightarrow x=6\)
Vậy \(x=6\)
Chúc bạn học tốt !!!
(3/4+x).1/2=4/5
3/4+x=4/5:1/2
3/4+x=8/5
x=8/5-3/4
x=17/20
b)420:[75-(x-10)]=21
75-(x-10)=420:21
75-(X-10)=20
X-10=75-20
X-10=55
X=55+10
X=65
K ĐÓ NHÉ
a) x/21=4/7+-7/3
x/21=-37/21
x =-37
Vậy x =-37
b)x/4+x/5=-9/10
x:4+x:5=-9/10
x.(-4)+x.(-5)=-9/10
x.(-4+(-5))=-9/10
x.(-9) =-9/10
x =-9/10:(-9)
x = 1/10
Vậy x =1/10
\(21-5\left(x-4\right)=10\)
\(5\left(x-4\right)=21-10\)
\(5\left(x-4\right)=11\)
\(x-4=\dfrac{11}{5}\)
\(x=\dfrac{11}{5}+4=\dfrac{31}{5}\)