tìm a,b: a -3 =1
9 b 18
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\(\frac{a}{9}-\frac{3}{b}=\frac{1}{18}\Rightarrow\frac{a.b}{9b}-\frac{27}{9b}=\frac{1}{18}\Rightarrow\frac{ab-27}{9b}=\frac{1}{18}\)
=> 18.﴾ab‐27﴿ = 9b => 2﴾ab‐27﴿ = b=> 2ab ‐54 ‐b = 0 => 2ab ‐ b= 54
=> ﴾2a‐1﴿.b = 54 => 2a‐1 ; b là ước của 54
Ư﴾54﴿ = {54;1; 27;2; 9; 6; 3; 18;}
Nhận thấy 2a ‐1 là số lẻ nên ta chỉ cần chọn các trường hợp:
Nếu 2a ‐1 = 1 => a = 1 => b = 54
Nếu 2a ‐1 = 27 => a = 14 => b = 2
Nếu 2a ‐1 = 9 => a = 5 => b = 6
Nếu 2a‐1 = 3 => a= 2 => b= 18
Vậy....
\(\dfrac{a}{9}-\dfrac{3}{b}=\dfrac{1}{18}\)
⇔ \(\dfrac{2a-1}{18}=\dfrac{3}{b}\)
⇒ \(\left(2a-1\right).b=18.3\)
⇔ \(\left(2a-1\right).b=54\)
Ta thấy \(2a-1\) là 1 số nguyên lẻ. Ta có các trường hợp sau:
TH1: \(\left\{{}\begin{matrix}2a-1=1\\b=54\end{matrix}\right.\) ⇔ \(\left\{{}\begin{matrix}a=1\\b=54\end{matrix}\right.\)
TH2: \(\left\{{}\begin{matrix}2a-1=3\\b=18\end{matrix}\right.\) ⇔ \(\left\{{}\begin{matrix}a=2\\b=18\end{matrix}\right.\)
TH3: \(\left\{{}\begin{matrix}2a-1=9\\b=6\end{matrix}\right.\) ⇔ \(\left\{{}\begin{matrix}a=5\\b=6\end{matrix}\right.\)
TH4: \(\left\{{}\begin{matrix}2a-1=27\\b=2\end{matrix}\right.\) ⇔ \(\left\{{}\begin{matrix}a=14\\b=2\end{matrix}\right.\)
TH5: \(\left\{{}\begin{matrix}2a-1=-1\\b=-54\end{matrix}\right.\) ⇔ \(\left\{{}\begin{matrix}a=0\\b=-54\end{matrix}\right.\)
TH6: \(\left\{{}\begin{matrix}2a-1=-3\\b=-18\end{matrix}\right.\) ⇔ \(\left\{{}\begin{matrix}a=-1\\b=-18\end{matrix}\right.\)
TH7: \(\left\{{}\begin{matrix}2a-1=-9\\b=-6\end{matrix}\right.\) ⇔ \(\left\{{}\begin{matrix}a=-4\\b=-6\end{matrix}\right.\)
TH8: \(\left\{{}\begin{matrix}2a-1=-27\\b=-2\end{matrix}\right.\) ⇔ \(\left\{{}\begin{matrix}a=-13\\b=-2\end{matrix}\right.\)
Vậy \(\left(a,b\right)\in\left\{\left(1;54\right);\left(2;18\right);\left(5;6\right);\left(14;2\right);\left(0;-54\right);\left(-1;-18\right);\left(-4;-6\right);\left(-13;-2\right)\right\}\)
\(a.5,6,10,11,15,18,14,16,19\)
\(b.6,9,13,18,24,31,39\)
\(c.1,3,9,27,81\)
\(d.1,3,6,8,16,28,42,62\)
\(\frac{a}{9}-\frac{3}{b}=\frac{1}{18}\)
\(\Leftrightarrow\frac{-3}{b}=\frac{1}{18}-\frac{a}{9}=\frac{1-2a}{18}\)
\(\Rightarrow b\left(1-2a\right)=-3\cdot18=-54\)
.... Đề có cho số nguyên không ạ ?
\(B=\dfrac{\left(a+3\right)^2}{2a^2+6a}\cdot\dfrac{1-6a-18}{a^2-9}\\ a,ĐK:a\ne0;a\ne\pm3\\ b,B=\dfrac{\left(a+3\right)^2}{2a\left(a+3\right)}\cdot\dfrac{-17-6a}{\left(a-3\right)\left(a+3\right)}=\dfrac{-17-6a}{2a\left(a-3\right)}\\ c,B=0\Leftrightarrow-17-6a=0\Leftrightarrow a=-\dfrac{17}{6}\left(tm\right)\\ d,B=1\Leftrightarrow-17-6a=2a^2-6a\\ \Leftrightarrow2a^2=-17\Leftrightarrow a\in\varnothing\)
a, \(-19-\left(2x-5\right)^3=-18\)
\(\Leftrightarrow\left(2x-5\right)^3=-1\)
\(\Leftrightarrow2x-5=-1\)
\(\Leftrightarrow2x=4\)
\(\Leftrightarrow x=2\)
b, \(\frac{x}{5}+\frac{1}{3}.\frac{9}{2}=\frac{-1}{5}\)
\(\Leftrightarrow\frac{x}{5}+\frac{3}{2}=\frac{-1}{5}\)
\(\Leftrightarrow\frac{x}{5}=\frac{-17}{10}\)
\(\Leftrightarrow10x=5.\left(-17\right)\)
\(\Leftrightarrow10x=-85\)
\(\Leftrightarrow x=\frac{-17}{2}\)
Bài 1:
a: \(\Leftrightarrow x\cdot\dfrac{3}{4}=-1\)
hay x=-4/3
b: =>x=4/8+3/7=1/2+3/7=7/14+6/14=13/14
Bài 3:
BCNN(16;32;5)=160
UCLN(16;32;5)=1