Tìm n∈\in∈Z,để:
2n+5⋮⋮⋮n-1
2n+5⋮n−12n+5⋮n-12n+5⋮n−1
Mà n−1⋮n−1n-1⋮n-1n−1⋮n−1
⇔{2n+5⋮n−12n−2⋮n−1\Leftrightarrow\left\{{}\begin{matrix}2n+5⋮n-1\\2n-2⋮n-1\end{matrix}\right.⇔⎩⎨⎧2n+5⋮n−12n−2⋮n−1
⇔7⋮n−1\Leftrightarrow7⋮n-1⇔7⋮n−1
⇔n−1∈Ư(7)\Leftrightarrow n-1\inƯ\left(7\right)⇔n−1∈Ư(7)
\(\Leftrightarrow\left[{}\begin{matrix}n-1=1\-1=7\-1=-1\-1=-7\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}n=2\=8\=0\=-6\end{matrix}\right.\)
Vậy ...
2x/6 = 3y/7 và x+y =29
Cho hai vectơ a→\overrightarrow{a}a=(2m-1;3) và b→\overrightarrow{b}b=(2;1-m). Tìm m để hai vectơ đó vuông góc với nhau?
a)3x+49=2x+11183x+\dfrac{4}{9}=2x+\dfrac{11}{18}3x+94=2x+1811
b)712+23:x=58\dfrac{7}{12}+\dfrac{2}{3}:x=\dfrac{5}{8}127+32:x=85
c)∣2,5−x∣−15=1,2|2,5-x|-\dfrac{1}{5}=1,2∣2,5−x∣−51=1,2
d)2x+1+2x+2=1922^{x+1}+2^{x+2}=1922x+1+2x+2=192
Tim x
Giúp mình với
Cho a,b,c>0.Cmr
ab+bc+ca≥a+bb+c+b+ca+b+1\dfrac{a}{b}+\dfrac{b}{c}+\dfrac{c}{a}\ge\dfrac{a+b}{b+c}+\dfrac{b+c}{a+b}+1ba+cb+ac≥b+ca+b+a+bb+c+1
Vẽ parabol
y=| x2 - 3|x| + 2 |
f) −130−115.13−113.11−...−15.3−13.1-\dfrac{1}{30}-\dfrac{1}{15.13}-\dfrac{1}{13.11}-...-\dfrac{1}{5.3}-\dfrac{1}{3.1}−301−15.131−13.111−...−5.31−3.11
2x.(x-1/7)=0
Tìm x
cho cosa =3/4.Tinh A= cos(3a/2)cos(a/2)
−14−−5+13−32−3−74+43=?-\dfrac{1}{4}--5+\dfrac{1}{3}-\dfrac{3}{2}-3-\dfrac{7}{4}+\dfrac{4}{3}=?−41−−5+31−23−3−47+34=?
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