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Gọi số cạnh của tam giác là n
Ta có: \(\frac{\left(n-2\right).180^0}{n}=156^0\)
\(\Leftrightarrow\left(n-2\right).180^0=156^0n\)
\(\Leftrightarrow180^0n-360^0=156^0n\)
\(\Leftrightarrow180^0n-156^0n=360^0\)
\(\Leftrightarrow24^0n=360^0\)
\(\Leftrightarrow n=15\)
Vậy đa giác đó có 15 cạnh
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(=3\left(xy-4\right)\)
b) \(=x^2\left(x-y\right)+4\left(x-y\right)=\left(x-y\right)\left(x^2+4\right)\)
c) \(=x^2-\left(y^2-12y+36\right)=x^2-\left(y-6\right)^2=\left(x-y+6\right)\left(x+y-6\right)\)
d) \(=\left(4p^2-36p+81\right)-25=\left(2p-9\right)^2-25=\left(2p-9-5\right)\left(2p-9+5\right)=4\left(p-7\right)\left(p-2\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có : \(x^2+x+13=y^2\)
\(\Leftrightarrow4\left(x^2+x+13\right)=4y^2\)
\(\Leftrightarrow4x^2+4x+52=4y^2\)
\(\Leftrightarrow\left(4x^2+4x+1\right)-4y^2=-51\)
\(\Leftrightarrow\left(2y\right)^2-\left(2x+1\right)^2=51\)
\(\Leftrightarrow\left(2y+2x+1\right)\left(2y-2x-1\right)=51\)
Rồi xét từng trường hợp là ra nha
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a. Phương trình có nghiệm \(x=1\) khi:
\(4.1-2=k^2+k\Leftrightarrow k^2+k-2=0\Rightarrow\left[{}\begin{matrix}k=1\\k=-2\end{matrix}\right.\)
b. Phương trình tương đương:
\(k^2x-4x=-k-2\)
\(\Leftrightarrow\left(k-2\right)\left(k+2\right)x=-\left(k+2\right)\)
- Phương trình có nghiệm duy nhất khi: \(\left(k-2\right)\left(k+2\right)\ne0\Leftrightarrow k\ne\pm2\)
- Phương trình có vô số nghiệm khi: \(\left\{{}\begin{matrix}\left(k-2\right)\left(k+2\right)=0\\-\left(k+2\right)=0\end{matrix}\right.\) \(\Leftrightarrow k=-2\)
- Phương trình vô nghiệm khi: \(\left\{{}\begin{matrix}\left(k-2\right)\left(k+2\right)=0\\-\left(k+2\right)\ne0\end{matrix}\right.\) \(\Leftrightarrow k=2\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
vì x^2+x-20= x^2-4x+5x-20=x(x-4)+5(x-4)=(x-4)(x+5)
nên phân thức bên phải sẽ = (x-4)/(x^2+x-20)
![](https://rs.olm.vn/images/avt/0.png?1311)
Câu 2:
a: \(\Leftrightarrow4x^2+4x+1-4x^2-3x=2x-2\)
=>x+1=2x-2
=>-x=-3
hay x=3
b: \(\Leftrightarrow x\left(x^2-2x-24\right)=0\)
\(\Leftrightarrow x\left(x-6\right)\left(x+4\right)=0\)
hay \(x\in\left\{0;6;-4\right\}\)
c: \(\Leftrightarrow x^2-3x+2-3x-6=-x-10\)
\(\Leftrightarrow-6x-4=-x-10\)
=>-5x=-6
hay x=6/5(nhận)
Câu 2 :
a, \(4x^2+4x+4-4x^2-3x=2x-2\Leftrightarrow x+4=2x-2\Leftrightarrow x=6\)
b, \(x\left(x^2-2x+1-25\right)=0\Leftrightarrow x\left(x-6\right)\left(x+4\right)=0\Leftrightarrow x=0;x=6;x=-4\)
c, đk : x khác 2 ; -2 \(\Rightarrow x^2-3x+2-3x-6=-x-10\)
\(\Leftrightarrow x^2-6x-4=-x-10\Leftrightarrow x^2-5x+6=0\Leftrightarrow\left(x-2\right)\left(x-3\right)=0\Leftrightarrow x=2\left(ktm\right);x=3\)
Bài 2 :
\(a,\left(x+2\right)\left(x^2+3x-2\right)=2\left(x+2\right)x^2\)
\(\Leftrightarrow\left(x+2\right)\left(x^2+3x-2\right)-2x^2\left(x+2\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(x^2+3x-2-2x^2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+2=0\\-x^2+3x-2=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-2\\-x^2+x+2x-2=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-2\\-x\left(x-1\right)+2\left(x-1\right)=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-2\\\left(x-1\right)\left(-x+2\right)=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-2\\\left[{}\begin{matrix}x-1=0\\-x+2=0\end{matrix}\right.\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-2\\\left[{}\begin{matrix}x=1\\x=2\end{matrix}\right.\end{matrix}\right.\)
Vậy \(S=\left\{-2;2;1\right\}\)
\(b,9x^2-\left(6x+2\right)\left(x-5\right)=1\)
\(\Leftrightarrow9x^2-\left(6x^2-30x+2x-10\right)-1=0\)
\(\Leftrightarrow9x^2-6x^2+30x-2x+10-1=0\)
\(\Leftrightarrow3x^2+28x+9=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{1}{3}\\x=-9\end{matrix}\right.\)
Vậy \(S=\left\{-\dfrac{1}{3};-9\right\}\)
\(c,\dfrac{x}{3x-2}-\dfrac{x}{2+3x}=\dfrac{6x^2}{9x^2-4}\left(dkxd:x\ne\pm\dfrac{2}{3}\right)\)
\(\Leftrightarrow\dfrac{x}{3x-2}-\dfrac{x}{3x+2}-\dfrac{6x^2}{\left(3x-2\right)\left(3x+2\right)}=0\)
\(\Leftrightarrow\dfrac{x\left(3x+2\right)-x\left(3x-2\right)-6x^2}{\left(3x-2\right)\left(3x+2\right)}=0\)
\(\Leftrightarrow3x^2+2x-3x^2+2x-6x^2=0\)
\(\Leftrightarrow4x-6x^2=0\)
\(\Leftrightarrow-2x\left(-2+3x\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}-2x=0\\-2+3x=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\left(tmdk\right)\\x=\dfrac{2}{3}\left(ktmdk\right)\end{matrix}\right.\)
Vậy \(S=\left\{0\right\}\)
Bài 1 :
\(a,P=\dfrac{x^2+x}{x^2-2x+1}:\left(\dfrac{x+1}{x}-\dfrac{1}{1-x}+\dfrac{2-x^2}{x^2-x}\right)\left(dkxd:x\ne0,x\ne\pm1\right)\)
\(=\dfrac{x^2+x}{\left(x-1\right)^2}:\left(\dfrac{x+1}{x}+\dfrac{1}{x-1}+\dfrac{2-x^2}{x\left(x-1\right)}\right)\)
\(=\dfrac{x^2+x}{\left(x-1\right)^2}:\left(\dfrac{x^2-1+x+2-x^2}{x\left(x-1\right)}\right)\)
\(=\dfrac{x\left(x+1\right)}{\left(x-1\right)^2}.\dfrac{x\left(x-1\right)}{x+1}\)
\(=\dfrac{x^2}{x-1}\left(dpcm\right)\)
\(b,P=-\dfrac{1}{2}\Rightarrow\dfrac{x^2}{x-1}=-\dfrac{1}{2}\)
\(\Rightarrow2x^2=-\left(x-1\right)\)
\(\Rightarrow2x^2=-x+1\)
\(\Rightarrow2x^2+x-1=0\)
\(\Rightarrow\left[{}\begin{matrix}x=\dfrac{1}{2}\\x=-1\end{matrix}\right.\)
Vậy \(P=-\dfrac{1}{2}\) thì \(x=\dfrac{1}{2};x=-1\)
\(c,\) Để P nhận giá trị nguyên dương thì \(P\ge0\)
\(\Leftrightarrow\dfrac{x^2}{x-1}\ge0\Leftrightarrow x\ge0\)