Trình bày rõ ra giúp mềnh nha
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Đk: tự tìm
\(pt\Leftrightarrow\sqrt{\left(x-4\right)\left(x+4\right)}+\sqrt{x-4}=0\)
\(\Leftrightarrow\sqrt{x-4}\left(\sqrt{x+4}+1\right)=0\)
Dễ thấy: \(\sqrt{x+4}\ge0\forall x\)
\(\Rightarrow\sqrt{x+4}+1\ge1>0\forall x\) (vô nghiệm)
\(\Rightarrow\sqrt{x-4}=0\Rightarrow x-4=0\Rightarrow x=4\)
![](https://rs.olm.vn/images/avt/0.png?1311)
giả sử 86:a=bdư9 =>a>9 và (86-9)=77 chia hết cho a
=> a=11 hoặc a=77
từ đó b=7 boặc b=1
chào!!!!
tk mk nha bn
![](https://rs.olm.vn/images/avt/0.png?1311)
Gọi số cần tìm là x
Theo đề, ta có:
-9<4x<-6
=>4x=-8
hay x=-2
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 2:
a: \(=\dfrac{3}{5}\cdot\dfrac{6}{7}=\dfrac{18}{35}\)
b: =3/5+8/25
=15/25+8/25
=23/25
Bài 3:
a: =>x=2/3*2/5=4/25
b: =>x=4/9*2/3=8/27
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a,\dfrac{2}{7}+\dfrac{1}{4}=\dfrac{8}{28}+\dfrac{7}{28}=\dfrac{15}{28}\\ b,\dfrac{3}{5}+\dfrac{3}{8}=\dfrac{3.8}{5.8}+\dfrac{3.5}{5.8}=\dfrac{6}{5}\\ c,=\dfrac{4.3}{9.3}+\dfrac{10}{27}=\dfrac{12+10}{27}=\dfrac{22}{27}\\ d,=\dfrac{2.3}{3.3}+\dfrac{7}{9}=\dfrac{6+7}{9}=\dfrac{13}{9}\\ e,=\dfrac{5.5}{12.5}+\dfrac{7.4}{15.4}=\dfrac{25+28}{60}=\dfrac{53}{60}\)
\(\dfrac{2}{7}+\dfrac{1}{4}=\dfrac{8}{28}+\dfrac{7}{28}=\dfrac{15}{28};\dfrac{3}{5}+\dfrac{3}{8}=\dfrac{24}{40}+\dfrac{15}{40};\dfrac{4}{9}+\dfrac{10}{27}=\dfrac{12}{27}+\dfrac{10}{27}=\dfrac{22}{27};\dfrac{2}{3}+\dfrac{7}{9}=\dfrac{18}{27}+\dfrac{21}{27}=\dfrac{39}{27};\dfrac{5}{12}+\dfrac{7}{15}=\dfrac{75}{180}+\dfrac{84}{180}=\dfrac{159}{180}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\text{Số số hạng của dãy là : }\left(100-1\right)\div3+1=34\left(\text{số}\right)\)
\(\text{Đặt }A=1+4+9+...+100\)
\(\Rightarrow A=\frac{\left(100+1\right).34}{2}=1717\)
\(\text{Vậy }1+4+9+...+100=1717\)
28.
\(\Leftrightarrow2x+1=x-1\)
\(\Leftrightarrow x=-2\)
29.
\(\Leftrightarrow x^3-2x^2-3x^2+6x=0\)
\(\Leftrightarrow x^2\left(x-2\right)-3x\left(x-2\right)=0\)
\(\Leftrightarrow\left(x-2\right)\left(x^2-3x\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-2=0\\x^2-3x=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=2\\x\left(x-3\right)=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=2\\x=0\\x=3\end{matrix}\right.\)
30.\(\Leftrightarrow3x^2+3x+2x+2=0\)
\(\Leftrightarrow3x\left(x+1\right)+2\left(x+1\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left(3x+2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+1=0\\3x+2=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-1\\x=-\dfrac{2}{3}\end{matrix}\right.\)
\(28,\\ \Leftrightarrow\left[{}\begin{matrix}2x+1=x-1\\2x+1=-x+1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-2\\3x=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=0\end{matrix}\right.\\ 29,\\ \Leftrightarrow x\left(x^2-5x+6\right)=0\\ \Leftrightarrow x\left(x^2-2x-3x+6\right)=0\\ \Leftrightarrow x\left[x\left(x-2\right)-3\left(x-2\right)\right]=0\\ \Leftrightarrow x\left(x-2\right)\left(x-3\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=0\\x=2\\x=3\end{matrix}\right.\)
\(30,\\ \Leftrightarrow3x^2+3x+2x+2=0\\ \Leftrightarrow3x\left(x+1\right)+2\left(x+1\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}3x+2=0\\x+1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{-2}{3}\\x=-1\end{matrix}\right.\)