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\(A=\frac{9}{7}\times\frac{13}{5}\times\frac{9}{4}=\frac{1053}{140}\)
\(B=\frac{27}{5}\times\frac{13}{7}\times\frac{1}{4}=\frac{351}{140}\)
Vậy \(\frac{A}{B}=A:B=\frac{1053}{140}:\frac{351}{140}=\frac{1053}{351}=3\)
\(\frac{-x}{4}=\frac{-9}{x}\)
\(\Rightarrow-x\cdot x=-9\cdot4\)
\(\Rightarrow-x^2=-36\)
\(\Rightarrow-x^2=-6^2\)
\(\Rightarrow-x=-6\)
\(\Rightarrow\) \(x=6\)
\(\frac{x-1}{9}=\frac{8}{3}\)
\(\Rightarrow\left(x-1\right)\cdot3=9\cdot8\)
\(\Rightarrow\) \(3x-3=72\)
\(\Rightarrow\) \(3x=72+3\)
\(\Rightarrow\) \(3x=75\)
\(\Rightarrow\) \(x=75\div3\)
\(\Rightarrow\) \(x=25\)
a) Ta có: \(\dfrac{-3}{5}x+\dfrac{-7}{4}=\dfrac{3}{10}\)
\(\Leftrightarrow\dfrac{-3}{5}x=\dfrac{3}{10}+\dfrac{7}{4}=\dfrac{41}{20}\)
\(\Leftrightarrow x=\dfrac{41}{20}:\dfrac{-3}{5}=\dfrac{41}{20}\cdot\dfrac{-5}{3}\)
hay \(x=-\dfrac{41}{12}\)
Vậy: \(x=-\dfrac{41}{12}\)
\(\frac{\frac{1}{3}+\frac{1}{9}-\frac{1}{27}}{\frac{5}{3}+\frac{5}{9}-\frac{5}{27}}=\frac{\frac{9}{27}+\frac{3}{27}-\frac{1}{27}}{\frac{45}{27}+\frac{15}{27}-\frac{5}{27}}=\frac{\frac{9+3-1}{27}}{\frac{45+15-5}{27}}=\frac{\frac{11}{27}}{\frac{55}{27}}=\frac{11}{55}=\frac{1}{5}.\)
a: Gọi a=UCLN(n+1;2n+3)
\(\Leftrightarrow2n+3-2\left(n+1\right)⋮a\)
\(\Leftrightarrow1⋮a\)
=>a=1
=>n+1/2n+3 là phân số tối giản
b: Gọi d=UCLN(2n+5;4n+8)
\(\Leftrightarrow4n+10-4n-8⋮d\)
\(\Leftrightarrow2⋮d\)
mà 2n+5 là số lẻ
nên n=1
=>2n+5/4n+8 là phân số tối giản
457+218+143=(457+143)+218=600+218=818
b/ 346 + 412 + 188=346+(412+188)=346+600=946
\(c,\dfrac{8}{9}+\dfrac{14}{27}+\dfrac{1}{9}=\left(\dfrac{8}{9}+\dfrac{1}{9}\right)+\dfrac{14}{27}=1+\dfrac{14}{27}=\dfrac{41}{27}\)
d,\(\dfrac{1}{2}+\dfrac{3}{4}+\dfrac{1}{2}=\left(\dfrac{1}{2}+\dfrac{1}{2}\right)+\dfrac{3}{4}=1+\dfrac{3}{4}=\dfrac{7}{4}\)e,3,17.8,9+8,9.6,83=8,9(3,17+6,83=8,9.10=89
a)
457 + 218 + 143
= (457 + 143) + 218
= 600 + 218
= 818
b)
346 + 412 + 188
=346 + (412 + 188)
=346 + 600
= 946
c)
\(\dfrac{8}{9}+\dfrac{14}{27}+\dfrac{1}{9}=\left(\dfrac{8}{9}+\dfrac{1}{9}\right)+\dfrac{14}{27}=1+\dfrac{14}{27}=\dfrac{27}{27}+\dfrac{14}{27}=\dfrac{41}{27}.\)
d)
\(\dfrac{1}{2}+\dfrac{3}{4}+\dfrac{1}{2}=\left(\dfrac{1}{2}+\dfrac{1}{2}\right)+\dfrac{3}{4}=1+\dfrac{3}{4}=\dfrac{4}{4}+\dfrac{3}{4}=\dfrac{7}{4}.\)
e)\(\)
3,17 x 8,9 + 8,9 x 6,83 = 8,9 x ( 3,17 + 6,83 )
= 8,9 x 10
= 89
f)
1+3+5+...+19
= (19+1)+(17+3)+(15+5)+(13+7)+(11+9)
= 20+20+20+20+20
= 20 x 5
= 100
\(\frac{1}{9}.3^2.3^2.3^n=3^7\)
\(3^n=3^5\)
n=5
\(\frac{1}{9}.27=3=3^n\)
n=1