(4x2-25)=(2x+5)(x-3)
g, 4x2 - 25 - (2x-5) (2x+7) = 0 i, x3+27+(x+3)(x-9) = 0
g) \(4x^2-25-\left(2x-5\right)\left(2x+7\right)=0\)
\(\Rightarrow\left(2x-5\right)\left(2x+5\right)-\left(2x-5\right)\left(2x+7\right)=0\)
\(\Rightarrow\left(2x-5\right)\left(2x+5-2x-7\right)=0\)
\(\Rightarrow-2\left(2x-5\right)=0\Rightarrow x=\dfrac{5}{2}\)
i) \(x^3+27+\left(x+3\right)\left(x-9\right)=0\)
\(\Rightarrow\left(x+3\right)\left(x^2-3x+9\right)+\left(x+3\right)\left(x-9\right)=0\)
\(\Rightarrow\left(x+3\right)\left(x^2-3x+9+x-9\right)=0\)
\(\Rightarrow\left(x+3\right)\left(x^2-2x\right)=0\Rightarrow x\left(x+3\right)\left(x-2\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=0\\x=-3\\x=2\end{matrix}\right.\)
(2x-5)(4x2+10x+25)(2x+5)(4x2-10x+25)-64x6
Ta có: \(\left(2x-5\right)\left(4x^2+10x+25\right)\left(2x+5\right)\left(4x^2-10x+25\right)-64x^6\)
\(=\left(8x^3-125\right)\left(8x^3+125\right)-64x^6\)
\(=64x^6-15625-64x^6\)
=-15625
Tìm x, biết:
(5-2x)(2x+7)=4x2-25
4(2x+7)2-9(x+3)2=0
\(\left(5-2x\right)\left(2x+7\right)=4x^2-25\)
\(\Leftrightarrow-\left(2x-5\right)\left(2x+7\right)=\left(2x-5\right)\left(2x+5\right)\)
\(\Leftrightarrow-2x-7=2x+5\)
\(\Leftrightarrow-4x=12\Leftrightarrow x=-3\)
\(4\left(2x+7\right)^2-9\left(x+3\right)^2=0\)
\(\Leftrightarrow\left[2\left(2x+7\right)\right]^2-\left[3\left(x+3\right)\right]^2=0\)
\(\Leftrightarrow\left[2\left(2x+7\right)-3\left(x+3\right)\right].\left[2\left(2x+7\right)+3\left(x+3\right)\right]=0\)
\(\Leftrightarrow\left(4x+14-3x-9\right)\left(4x+14+3x+9\right)=0\)
\(\Leftrightarrow\left(x+5\right)\left(7x+23\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+5=0\\7x+23=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-5\\x=-\frac{23}{7}\end{matrix}\right.\)
b/\(4\left(2x+7\right)^2-9\left(x+3\right)^2=0\)
\(\Leftrightarrow4\left(4x^2+28x+49\right)-9\left(x^2+6x+9\right)=0\)
\(\Leftrightarrow16x^2+112x+196-9x^2-36x-81=0\)
\(\Leftrightarrow7x^2+76x+115=0\)
\(\Leftrightarrow x=\frac{-38\pm3\sqrt{71}}{7}\)
Vậy ..
Bài 5: Tìm nghiệm của các đa thức sau: Dạng 1: a) 4x + 9 b) -5x + 6 c) 7 – 2x d) 2x + 5 Dạng 2: a) ( x+ 5 ) ( x – 3) b) ( 2x – 6) ( x – 3) c) ( x – 2) ( 4x + 10 ) Dạng 3: a) x2 -2x b) x2 – 3x c) 3x2 – 4x d) ( 2x- 1)2 Dạng 4: a) x2 – 1 b) x2 – 9 c)– x 2 + 25 d) x2 - 2 e) 4x2 + 5 f) –x 2 – 16 g) - 4x4 – 25 Dạng 5: a) 2x2 – 5x + 3 b) 4x2 + 6x – 1 c) 2x2 + x – 1 d) 3x2 + 2x – 1
Bài 1. Giải các phương trình sau:
a) |4x2 - 25| = 0
b) |x - 2| = 3
c) |x - 3| = 2x - 1
d) |x - 5| = |3x - 2|
Lời giải:
a) $|4x^2-25|=0$
$\Leftrightarrow 4x^2-25=0$
$\Leftrightarrow (2x-5)(2x+5)=0$
$\Rightarrow x=\pm \frac{5}{2}$
b)
$|x-2|=3$
\(\Rightarrow \left[\begin{matrix} x-2=-3\\ x-2=3\end{matrix}\right.\Rightarrow \left[\begin{matrix} x=-1\\ x=5\end{matrix}\right.\)
c)
\(|x-3|=2x-1\Rightarrow \left\{\begin{matrix} 2x-1\geq 0\\ \left[\begin{matrix} x-3=2x-1\\ x-3=1-2x\end{matrix}\right.\end{matrix}\right.\)
\(\Leftrightarrow \left\{\begin{matrix} x\geq \frac{1}{2}\\ \left[\begin{matrix} x=-2\\ x=\frac{4}{3}\end{matrix}\right.\end{matrix}\right.\Rightarrow x=\frac{4}{3}\)
d)
$|x-5|=|3x-2|$
\(\Rightarrow \left[\begin{matrix} x-5=3x-2\\ x-5=2-3x\end{matrix}\right.\Leftrightarrow \left[\begin{matrix} x=\frac{-3}{2}\\ x=\frac{7}{4}\end{matrix}\right.\)
Giúp tui 2 câu này với
1) (x3 - 4x2) - (x - 4) = 0
2) (4x2 - 25)2 - 9(2x - 5)2
1: Ta có: \(\left(x^3-4x^2\right)-\left(x-4\right)=0\)
\(\Leftrightarrow\left(x-4\right)\left(x+1\right)\left(x-1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=4\\x=1\\x=-1\end{matrix}\right.\)
Bài 1: tìm x, biết:
1, (x-1)(x+2)-(x-1)2=0
2, (x-2)2-3(x-2)(x+1)=0
3, (5-2x)(2x+7)=4x2-25
1, \(\left(x-1\right)\left(x+2\right)-\left(x-1\right)^2=0\)
\(\Leftrightarrow\left(x-1\right)\left[x+2-\left(x-1\right)\right]=0\)
\(\Leftrightarrow3\left(x-1\right)=0\Leftrightarrow x=1\)
2, \(\left(x-2\right)^2-3\left(x-2\right)\left(x+1\right)=0\)
\(\Leftrightarrow\left(x-2\right)\left[x-2-3\left(x+1\right)\right]=0\)
\(\Leftrightarrow\left(x-2\right)\left(-2x-5\right)=0\Leftrightarrow x=-\dfrac{5}{2};x=2\)
3, \(\left(5-2x\right)\left(2x+7\right)=4x^2-25=\left(2x-5\right)\left(2x+5\right)\)
\(\Leftrightarrow\left(5-2x\right)\left(2x+7\right)+\left(5-2x\right)\left(2x+5\right)=0\)
\(\Leftrightarrow\left(5-2x\right)\left(2x+7+2x+5\right)=0\Leftrightarrow\left(4x+12\right)\left(5-2x\right)=0\Leftrightarrow x=-3;x=\dfrac{5}{2}\)
1) Ta có: \(\left(x-1\right)\left(x+2\right)-\left(x-1\right)^2=0\)
\(\Leftrightarrow\left(x-1\right)\left(x+2-x+1\right)=0\)
\(\Leftrightarrow x-1=0\)
hay x=1
2) Ta có: \(\left(x-2\right)^2-3\left(x-2\right)\left(x+1\right)=0\)
\(\Leftrightarrow\left(x-2\right)\left(x-2-3x-3\right)=0\)
\(\Leftrightarrow\left(x-2\right)\left(-2x-5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=2\\x=\dfrac{-5}{2}\end{matrix}\right.\)
giải các phương trình:
a) |4x2−25|=0|4x2−25|=0
b) |x−2|=3|x−2|=3
c) |x−3|=2x−1|x−3|=2x−1
d) |x+5|=|3x−2|
a) \(\left|4x^2-25\right|=0\)
\(\Leftrightarrow4x^2-25=0\)
\(\Leftrightarrow\left(2x+5\right)\left(2x-5\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}2x-5=0\\2x+5=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=\frac{5}{2}\\x=-\frac{5}{2}\end{cases}}}\)
Tìm x, biết :
a) (x+4)2-x2(x+12)=16
c) (x+3)3-x(3x+1)2+(2x+1)(4x2-2x+1)=28
d) (x-2)3-(x+5)(x2-5x+25)-6x2=11
c: Ta có: \(\left(x+3\right)^3-x\left(3x+1\right)^2+\left(2x+1\right)\left(4x^2-2x+1\right)=28\)
\(\Leftrightarrow x^3+9x^2+27x+27-9x^3-6x^2-x+8x^3+1=28\)
\(\Leftrightarrow3x^2+26x=0\)
\(\Leftrightarrow x\left(3x+26\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=-\dfrac{26}{3}\end{matrix}\right.\)
\(a,\Leftrightarrow x^2+8x+16-x^3-12x^2=16\\ \Leftrightarrow x^3+11x^2-8x=0\\ \Leftrightarrow x\left(x^2+11x-8\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x^2+11x-8=0\left(1\right)\end{matrix}\right.\\ \Delta\left(1\right)=121+32=153\\ \Leftrightarrow\left[{}\begin{matrix}x=\dfrac{-11-3\sqrt{17}}{2}\\x=\dfrac{-11+3\sqrt{17}}{2}\end{matrix}\right.\\ S=\left\{0;\dfrac{-11-3\sqrt{17}}{2};\dfrac{-11+3\sqrt{17}}{2}\right\}\)
\(c,\Leftrightarrow x^3+9x^2+27x+27-9x^3-6x^2-x+8x^3+1=28\\ \Leftrightarrow3x^2+26x=0\\ \Leftrightarrow x\left(3x+26\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=-\dfrac{26}{3}\end{matrix}\right.\\ d,\Leftrightarrow x^3-6x^2+12x-8-x^3-125-6x^2=11\\ \Leftrightarrow-12x^2+12x-144=0\\ \Leftrightarrow x^2-x+12=0\Leftrightarrow\left[{}\begin{matrix}x=4\\x=3\end{matrix}\right.\)
4x2-3(2x-5)-25=0
\(4x^2-3\left(2x-5\right)-25=0\Leftrightarrow4x^2-6x-10=0\)
\(\Leftrightarrow2\left(2x^2-3x-5\right)=0\Leftrightarrow2\left(x+1\right)\left(2x-5\right)=0\Leftrightarrow x=-1;x=\dfrac{5}{2}\)
4x2-3(2x-5)-25=0
⇒(2x)2-52-3(2x-5)=0
⇒(2x-5)(2x+5)-3(2x-5)=0
⇒(2x-5)(2x+2)=0
⇒hoặc 2x-5=0⇒x=2,5
hoặc 2x+2=0⇒x=-1
vậy x={2,5;-1}