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x3 + 2x2 + 2x +1 = 0
(=) x3 + x2 +x2 + x + x + 1 = 0
(=) x2.(x+1) + x.(x+1) + (x+1) = 0
(=) (x2 + x +1 ).(x+1) = 0
(=) \(\orbr{\begin{cases}x+1=0\\x^2+x+1=0\left(lo\text{ại}\right)\end{cases}}\)(=) x=-1
Vậy phương trình có nghiệm là x=-1
a/ Đặt (x^2 - 5x) = a thì ta có
a^2 + 10a + 24 = 0
<=> (a + 4)(a + 6) = 0
Làm nốt
b/ (x - 4)(x - 5)(x - 6)(x - 7) = 1680
<=> (x - 4)(x - 7)(x - 5)(x - 6) = 1680
<=> (x^2 - 11x + 28)(x^2 - 11x + 30) = 1680
Đặt x^2 - 11x + 28 = a thì ta có
a(a + 2) = 1680
<=> (a - 40)(a + 42) = 0
Làm nốt
a/ \(x^3+1+2x^2+2x=0\Leftrightarrow\left(x+1\right)\left(x^2-x+1\right)+2x\left(x+1\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left(x^2+x+1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+1=0\\x^2+x+1=0\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=-1\\\left(x+\frac{1}{2}\right)^2+\frac{3}{4}=0\left(vn\right)\end{matrix}\right.\)
b/ \(\left(x-4\right)\left(x-7\right)\left(x-5\right)\left(x-6\right)-1680=0\)
\(\Leftrightarrow\left(x^2-11x+28\right)\left(x^2-11x+30\right)-1680=0\)
Đặt \(x^2-11x+28=a\Rightarrow x^2-11x+30=a+2\)
Pt trở thành:
\(a\left(a+2\right)-1680=0\Leftrightarrow a^2-2a-1680=0\) \(\Rightarrow\left[{}\begin{matrix}a=42\\a=-40\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x^2-11x+28=42\\x^2-11x+28=-40\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x^2-11x-14=0\\x^2-11x+68=0\left(vn\right)\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=\frac{11+\sqrt{177}}{2}\\x=\frac{11-\sqrt{177}}{2}\end{matrix}\right.\)
Ta có : |x - 2| + |x - 3| + |x - 4| + |x - 5| + |x - 6| -x + 7 = 0
=> |x - 2| + |x - 3| + |x - 4| + |x - 5| + |x - 6| = x - 7
ĐK \(x-7\ge0\Rightarrow x\ge7\)
Khi đó ta có x - 2 > 0 ; x - 3 > 0 ; ... x - 6 > 0
=> |x - 2| + |x - 3| + |x - 4| + |x - 5| + |x - 6| = x - 7
<=> x - 2 + x - 3 + x - 4 + x - 5 + x - 6 = x - 7
=> 5x - 20 = x - 7
=> 4x = 13
=> x = 4,25 (loại)
Vậy x \(\in\varnothing\)
Bài 3:
a) \(\left(x-6\right).\left(2x-5\right).\left(3x+9\right)=0\)
\(\Leftrightarrow\left(x-6\right).\left(2x-5\right).3.\left(x+3\right)=0\)
Vì \(3\ne0.\)
\(\Leftrightarrow\left[{}\begin{matrix}x-6=0\\2x-5=0\\x+3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=6\\2x=5\\x=-3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=6\\x=\frac{5}{2}\\x=-3\end{matrix}\right.\)
Vậy phương trình có tập hợp nghiệm là: \(S=\left\{6;\frac{5}{2};-3\right\}.\)
b) \(2x.\left(x-3\right)+5.\left(x-3\right)=0\)
\(\Leftrightarrow\left(x-3\right).\left(2x+5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-3=0\\2x+5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\2x=-5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=-\frac{5}{2}\end{matrix}\right.\)
Vậy phương trình có tập hợp nghiệm là: \(S=\left\{3;-\frac{5}{2}\right\}.\)
c) \(\left(x^2-4\right)-\left(x-2\right).\left(3-2x\right)=0\)
\(\Leftrightarrow\left(x^2-2^2\right)-\left(x-2\right).\left(3-2x\right)=0\)
\(\Leftrightarrow\left(x-2\right).\left(x+2\right)-\left(x-2\right).\left(3-2x\right)=0\)
\(\Leftrightarrow\left(x-2\right).\left(x+2-3+2x\right)=0\)
\(\Leftrightarrow\left(x-2\right).\left(3x-1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-2=0\\3x-1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\3x=1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=\frac{1}{3}\end{matrix}\right.\)
Vậy phương trình có tập hợp nghiệm là: \(S=\left\{2;\frac{1}{3}\right\}.\)
Chúc bạn học tốt!
\(\left(x-2\right)^2+\left|x-5\right|-x^2-14=0.\)
\(\left(x^2-4x+4\right)+\left|x-5\right|-x^2-14=0.\)
\(x\text{}\text{}\text{}^2-4x+4+\left|x-5\right|-x^2-14=0.\)
\(x\text{}\text{}\text{}^2-x^2-4x+4-14+\left|x-5\right|=0.\)
\(-4x-10+\left|x-5\right|=0\)
.. đến đây xét tiếp để ra kq ạ -,-
a, \(\left(x-4\right)\left(x-5\right)\left(x-6\right)\left(x-7\right)=1680\)
\(\Leftrightarrow\left[\left(x-4\right)\left(x-7\right)\right]\left[\left(x-5\right)\left(x-6\right)\right]=1680\)
\(\Leftrightarrow\left(x^2-11x+28\right)\left(x^2-11x+30\right)=1680\)
Gọi \(k=x^2-11x+29\)
\(\Rightarrow\left(k-1\right)\left(k+1\right)=1680\)
\(\Rightarrow k^2-1=1680\Rightarrow k^2=1681\)
\(\Rightarrow k=\sqrt{1681}=\pm41\)
* TH1: k = -41
\(\Leftrightarrow x^2-11x+29=-41\)
\(\Leftrightarrow x^2-11x+70=0\)
\(\Leftrightarrow x^2-2.\dfrac{11}{2}x+\dfrac{121}{4}-\dfrac{121}{4}+70=0\)
\(\Leftrightarrow\left(x-\dfrac{11}{2}\right)^2+\dfrac{159}{4}=0\Leftrightarrow\left(x-\dfrac{11}{2}\right)^2=\dfrac{-159}{4}\left(vôli\right)\)
Vì \(\left(x-\dfrac{11}{2}\right)^2\ge0\forall x\) mà \(\dfrac{-159}{4}< 0\Rightarrow\left(x-\dfrac{11}{2}\right)^2=\dfrac{-159}{4}\left(loại\right)\)
* TH2: k = 41
\(\Leftrightarrow x^2-11x+29=41\)
\(\Leftrightarrow x^2-11x-12=0\)
\(\Leftrightarrow x^2+x-12x-12=0\)
\(\Leftrightarrow x\left(x+1\right)-12\left(x+1\right)=0\)
\(\Leftrightarrow\left(x-12\right)\left(x+1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-12=0\\x+1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=12\\x=-1\end{matrix}\right.\)
\(\Rightarrow\left\{x_1=-1;x_2=12\right\}\)
b, \(\left(x+2\right)\left(x+3\right)\left(x-5\right)\left(x-6\right)=180\)
\(\Leftrightarrow\left[\left(x+2\right)\left(x-5\right)\right]\left[\left(x+3\right)\left(x-6\right)\right]=180\)
\(\Leftrightarrow\left(x^2-3x-10\right)\left(x^2-3x-18\right)=180\)
Đặt \(k=x^2-3x-14\)
Ta có pt: \(\left(k-4\right)\left(k+4\right)=180\)
\(\Leftrightarrow k^2-16=180\Leftrightarrow k^2=196\)
\(\Leftrightarrow k=\sqrt{196}=\pm14\)
* TH1: \(t=14\Leftrightarrow x^2-3x-14=14\)
\(\Leftrightarrow x^2-3x-28=0\)
\(\Leftrightarrow\left(x+4\right)\left(x-7\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+4=0\\x-7=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-4\\x=7\end{matrix}\right.\)
* TH2: \(t=-14\Leftrightarrow x^2-3x-14=-14\)
\(\Leftrightarrow x^2-3x=0\Leftrightarrow x\left(x-3\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x-3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=3\end{matrix}\right.\)
\(\Rightarrow\left\{x_1=-4;x_2=7;x_3=0;x_4=3\right\}\)