Làm hộ bài 3 với 5 ạ
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c: \(3x\left(x-7\right)-2\left(x-7\right)=0\)
\(\Leftrightarrow\left(x-7\right)\left(3x-2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=7\\x=\dfrac{2}{3}\end{matrix}\right.\)
d: \(7x^2-28=0\)
\(\Leftrightarrow\left(x-2\right)\left(x+2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-2\end{matrix}\right.\)
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Bài 1:
a: =8xy/2x=4y
b: \(=\dfrac{4x-1-7x+1}{3x^2y}=\dfrac{-3x}{3x^2y}=\dfrac{-1}{xy}\)
c: \(=\dfrac{3x-x+6}{2x\left(x+3\right)}=\dfrac{2\left(x+3\right)}{2x\left(x+3\right)}=\dfrac{1}{x}\)
e: \(=\dfrac{5\left(x+2\right)}{4\left(x-2\right)}\cdot\dfrac{-2\left(x-2\right)}{x+2}=\dfrac{-10}{4}=-\dfrac{5}{2}\)
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2/
a/
\(\dfrac{4n+2}{n+1}=\dfrac{4n+4-2}{n+1}=\dfrac{4\left(n+1\right)-2}{n+1}=4-\dfrac{2}{n+1}\)
\(\Rightarrow4n+2⋮n+1\) Khi \(n+1=\left\{-2;-1;1;2\right\}\Rightarrow n=\left\{-3;-2;0;1\right\}\)
b/
\(\Rightarrow a+2=\dfrac{8}{b-1}\left(b\ne1\right)\) (1)
a nguyên => a+2 nguyên \(\Rightarrow8⋮\left(b-1\right)\)
\(\Rightarrow b-1=\left\{-8;-4;-2;-1;1;2;4;8\right\}\)
\(\Rightarrow b=\left\{-7;-3;-1;0;2;3;5;9\right\}\) Thay các giá trị của b vào (1) để tìm a
3/
Gọi số tiền mẹ cho Chi là A \(\Rightarrow100000\le A\le200000\)
Nếu bớt số tiền mẹ cho Chi đi 5000 đồng thì
\(A-5000⋮15000;A-5000⋮8000\)
\(\Rightarrow A-5000=UC\left(8000;15000\right)\) Và \(95000\le A-5000\le195000\)
\(\Rightarrow A-5000=120000\Rightarrow A=125000\)
Bài 5:
Ta có: a+b+c=0
\(\Leftrightarrow\left\{{}\begin{matrix}a+b=-c\\a+c=-b\\b+c=-a\end{matrix}\right.\)
Ta có: \(A=a\left(a+b\right)\left(a+c\right)=a\cdot\left(-c\right)\cdot\left(-b\right)=abc\)
\(B=b\left(b+c\right)\left(a+b\right)=b\cdot\left(-a\right)\cdot\left(-c\right)=abc\)
\(C=c\left(a+c\right)\left(b+c\right)=c\cdot\left(-b\right)\cdot\left(-a\right)=abc\)
Do đó: A=B=C
Nó có bị sai ko á ?
E lm như này![undefined](https://hoc24.vn/images/discuss/1631343747_613c5483e5273.jpg)