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H
1
4 tháng 5 2016
(x+1)(x+2)(x+3)(x+4)=24
(x+1)(x+4)(x+2)(x+3)=24
(x\(^2\)+5x+4)(x2 +5x+6)=24
Đặt x2+5x+5=t
\(\Rightarrow\)(t+1)(t-1)=24
\(\Rightarrow\) t2 -1=24
\(\Rightarrow\) t2-25=0
\(\Rightarrow\) (t-5)(t+5)=0
\(\Rightarrow\) (x2+5x)(x2+5x+10)=0
\(\Rightarrow\) x(x+5)(x+5)2=0
\(\Rightarrow\) x(x+5)3=0
\(\Rightarrow\) x=0 hoặc (x+5)3=0
Vậy x=0 hoặc x= -5
DH
6 tháng 9 2017
\(\left(x^2+3x+2\right)\left(x^2+7x+12\right)=24\)
\(\Rightarrow\left(x^2+x+2x+2\right)\left(x^2+3x+4x+12\right)-24=0\)
\(\Rightarrow\left(x+1\right)\left(x+2\right)\left(x+3\right)\left(x+4\right)-24=0\)
\(\Rightarrow\left[\left(x+1\right)\left(x+4\right)\right]\left[\left(x+2\right)\left(x+3\right)\right]-24=0\)
\(\Rightarrow\left(x^2+5x+4\right)\left(x^2+5x+6\right)-24=0\)
Đặt \(x^2+5x+4=t\Rightarrow x^2+5x+6=t+2\) ta được:
\(t\left(t+2\right)-24=0\Rightarrow t^2+2t-24=0\)
\(\Rightarrow t^2-4t+6t-24=0\Rightarrow\left(t-4\right)\left(t-6\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}t-4=0\\t-6=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}t=4\\t=6\end{matrix}\right.\)
Vì \(t=x^2+5x+4\) nên
\(\left[{}\begin{matrix}x^2+5x+4=4\\x^2+5x+6=6\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x\left(x+5\right)=0\\x\left(x+5\right)=0\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}\left[{}\begin{matrix}x=0\\x=-5\end{matrix}\right.\\\left[{}\begin{matrix}x=0\\x=-5\end{matrix}\right.\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x=-5\end{matrix}\right.\)
Vậy................
Chúc bạn học tốt!!!
PT
3
NV
Nguyễn Việt Lâm
Giáo viên
8 tháng 2 2020
a/ \(\Leftrightarrow\left(x+1\right)\left(x+2\right)\left(x+3\right)\left(x+4\right)=24\)
\(\Leftrightarrow\left(x^2+5x+4\right)\left(x^2+5x+6\right)-24=0\)
\(\Leftrightarrow\left(x^2+5x+4\right)^2+2\left(x^2+5x+4\right)-24=0\)
\(\Leftrightarrow\left(x^2+5x\right)\left(x^2+5x+10\right)=0\)
b/ ĐKXĐ; ...
\(\Leftrightarrow\frac{x^2}{x^2+4x+4}+12x+5=3x^2+6x+2\)
\(\Leftrightarrow\frac{x^2+\left(12x+5\right)\left(x^2+4x+4\right)}{x^2+4x+4}=3x^2+6x+2\)
\(\Leftrightarrow\frac{\left(4x+10\right)\left(3x^2+6x+2\right)}{x^2+4x+4}=3x^2+6x+2\)
\(\Leftrightarrow\left[{}\begin{matrix}3x^2+6x+2=0\\\frac{4x+10}{x^2+4x+4}=1\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}3x^2+6x+2=0\\x^2=6\end{matrix}\right.\)
8 tháng 2 2020
a) Ta có :
(x2 + 3x + 2)(x2 + 7x + 12) = 24
⇔ ( x + 1 ) ( x + 2 ) (x + 3 ) ( x + 4 ) = 24
⇔ ( x + 1 ) ( x + 4 ) ( x + 2 ) ( x + 3 ) - 24 = 0
⇔ ( x2 + 5x + 4 ) ( x2 + 5x + 6 ) - 24 = 0
Đặt t = x2 + 5x + 4, ta có :
t ( t + 2 ) - 24 = 0
⇔ t2 + 2t +1 - 25 = 0
⇔ ( t + 1 )2 - 52 = 0
⇔ ( t - 4 ) ( t + 6 ) = 0
\(\Leftrightarrow\left[{}\begin{matrix}t-4=0\\t+6=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}t=4\\t=-6\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x^2+5x+4=4\\x^2+5x+4=-6\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x^2+5x=0\\x^2+5x+10=0\end{matrix}\right.\)
Sau đó tìm x bạn tự làm nha
Ý b) là - 3 à !?
A
3
AH
Akai Haruma
Giáo viên
28 tháng 2 2019
4.
\((2x+7)(x+3)^2(2x+5)=18\)
\(\Leftrightarrow [(2x+7)(2x+5)](x+3)^2=18\)
\(\Leftrightarrow (4x^2+24x+35)(x^2+6x+9)=18\)
\(\Leftrightarrow [4(x^2+6x+9)-1](x^2+6x+9)=18\)
\(\Leftrightarrow (4a-1)a=18\) (đặt \(x^2+6x+9=a\) )
\(\Leftrightarrow 4a^2-a-18=0\)
\(\Leftrightarrow (4a-9)(a+2)=0\Rightarrow \left[\begin{matrix} a=\frac{9}{4}\\ a=-2\end{matrix}\right.\)
Nếu \(a=x^2+6x+9=\frac{9}{4}\Leftrightarrow (x+3)^2=\frac{9}{4}\)
\(\Rightarrow \left[\begin{matrix} x+3=\frac{3}{2}\\ x+3=\frac{-3}{2}\end{matrix}\right.\Rightarrow \left[\begin{matrix} x=\frac{-3}{2}\\ x=\frac{-9}{2}\end{matrix}\right.\)
Nếu \(a=x^2+6x+9=-2\Leftrightarrow (x+3)^2=-2< 0\) (vô lý)
Vậy ............
AH
Akai Haruma
Giáo viên
28 tháng 2 2019
5.
PT \(\Leftrightarrow (x-1)(x-2)(2x-3)(2x-5)=30\)
\(\Leftrightarrow [(x-1)(2x-5)][(x-2)(2x-3)]=30\)
\(\Leftrightarrow (2x^2-7x+5)(2x^2-7x+6)=30\)
Đặt \(2x^2-7x+5=a\) thì:
PT \(\Leftrightarrow a(a+1)=30\)
\(\Leftrightarrow a^2+a-30=0\)
\(\Leftrightarrow (a-5)(a+6)=0\Rightarrow \left[\begin{matrix} a-5=0\\ a+6=0\end{matrix}\right.\)
Nếu \(a-5=0\Leftrightarrow 2x^2-7x=0\Leftrightarrow x(2x-7)=0\)
\(\Rightarrow \left[\begin{matrix} x=0\\ x=\frac{7}{2}\end{matrix}\right.\)
Nếu \(a+6=0\Leftrightarrow 2x^2-7x+11=0\)
\(\Leftrightarrow 2(x-\frac{7}{4})^2+\frac{39}{8}=0\Leftrightarrow 2(x-\frac{7}{4})^2=-\frac{39}{8}<0\) (vô lý)
Vậy...........
15 tháng 7 2021
a) \(\left(3x-2\right)\left(3x-1\right)=\left(3x+1\right)^2\)
<=> \(9x^2-9x+2=9x^2+6x+1\)
<=> \(15x=1\) <=> \(x=\frac{1}{15}\)
b) \(\left(4x-1\right)\left(x+1\right)=\left(2x-3\right)^2\)
<=> \(4x^2+3x-1=4x^2-12x+9\)
<=> \(15x^2=10\) <=> \(x=\frac{2}{3}\)
c) \(\left(5x+1\right)^2=\left(7x-3\right)\left(7x+2\right)\) <=> \(25x^2+10x+1=49x^2-7x-6\)
<=> \(24x^2-17x-7=0\) <=> \(24x^2-24x+7x-7=0\)
<=> \(\left(24x+7\right)\left(x-1\right)=0\) <=> \(\orbr{\begin{cases}x=-\frac{7}{24}\\x=1\end{cases}}\)
15 tháng 7 2021
d) (4 - 3x)(4 + 3x) = (9x - 3)(1 - x)
<=> 16 - 9x2 = 12x - 9x2 - 3
<=> 12x = 19
<=> x = 19/12
e) x(x + 1)(x + 2)(x + 3) = 24
<=> (x2 + 3x)(x2 + 3x + 2) = 24
<=> (x2 + 3x)2 + 2(x2 + 3x) - 24 = 0
<=> (x2 + 3x)2 + 6(x2 + 3x) - 4(x2 + 3x) - 24 = 0
<=> (x2 + 3x + 6)(x2 + 3x - 4) = 0
<=> \(\orbr{\begin{cases}x^2+3x+6=0\\x^2+3x-4=0\end{cases}}\)
<=> \(\orbr{\begin{cases}\left(x+\frac{3}{2}\right)^2+\frac{15}{4}=0\left(vn\right)\\\left(x+4\right)\left(x-1\right)=0\end{cases}}\)
<=> \(\orbr{\begin{cases}x=-4\\x=1\end{cases}}\)
g) (7x - 2)2 = (7x - 3)(7x + 2)
<=> 49x2 - 28x + 4 = 49x2 - 7x - 6
<=> 21x = 10 <=> x = 10/21
TM
11 tháng 8 2021
1/ \(7x-5=13-5x\)
\(\Leftrightarrow12x=18\)
\(\Leftrightarrow x=\dfrac{3}{2}\)
Vậy: \(S=\left\{\dfrac{3}{2}\right\}\)
==========
2/ \(19+3x=5-18x\)
\(\Leftrightarrow21x=-14\)
\(\Leftrightarrow x=-\dfrac{2}{3}\)
Vậy: \(S=\left\{-\dfrac{2}{3}\right\}\)
==========
3/ \(x^2+2x-4=-12+3x+x^2\)
\(\Leftrightarrow-x=-8\)
\(\Leftrightarrow x=8\)
Vậy: \(S=\left\{8\right\}\)
===========
4/ \(-\left(x+5\right)=3\left(x-5\right)\)
\(\Leftrightarrow-x-5=3x-15\)
\(\Leftrightarrow-4x=-10\)
\(\Leftrightarrow x=\dfrac{5}{2}\)
Vậy: \(S=\left\{\dfrac{5}{2}\right\}\)
==========
5/ \(3\left(x+4\right)=\left(-x+4\right)\)
\(\Leftrightarrow3x+12=-x+4\)
\(\Leftrightarrow4x=-8\)
\(\Leftrightarrow x=-2\)
Vậy: \(S=\left\{-2\right\}\)
[----------]
NT
11 tháng 8 2021
1. \(7x-5=13-5x\) \(\Leftrightarrow12x=18\Leftrightarrow x=\dfrac{3}{2}\)
2. \(19+3x=5-18x\Leftrightarrow21x=-14\Leftrightarrow x=-\dfrac{2}{3}\)
3. \(x^2+2x-4=-12+3x+x^2\Leftrightarrow-x=-8\Leftrightarrow x=8\)
4. \(-\left(x+5\right)=3\left(x-5\right)\Leftrightarrow-x-5=3x-15\Leftrightarrow4x=10\Leftrightarrow x=\dfrac{5}{2}\)
5. \(3\left(x+4\right)=-x+4\Leftrightarrow3x+12=-x+4\Leftrightarrow4x=-8\Leftrightarrow x=-2\)
\(\left(x^2+3x+2\right)\left(x^2+7x+12\right)=24\)
\(\Rightarrow\left(x+1\right)\left(x+2\right)\left(x+3\right)\left(x+4\right)=24\)
\(\Rightarrow\left(x+1\right)\left(x+4\right)\left(x+2\right)\left(x+3\right)=24\)
\(\Rightarrow\left(x^2+4x+x+4\right)\left(x^2+3x+2x+6\right)=24\)
\(\Rightarrow\left(x^2+5x+4\right)\left(x^2+5x+6\right)=24\)
\(\Rightarrow\left(x^2+5x+5-1\right)\left(x^2+5x+5+1\right)=24\)
\(\Rightarrow\left(x^2+5x+5\right)^2-1=24\)
\(\Rightarrow\left(x^2+5x+5\right)^2=25\)
\(\Rightarrow\left(x^2+5x+5\right)^2-25=0\)
\(\Rightarrow\left(x^2+5x+5+5\right)\left(x^2+5x+5-5\right)=0\)
\(\Rightarrow\left(x^2+5x+10\right)\left(x^2+5x\right)=0\)
\(\Rightarrow\left(x^2+5x+\dfrac{25}{4}+\dfrac{15}{4}\right)\left(x^2+5x\right)=0\)
\(\Rightarrow\left[\left(x^2+5x+\dfrac{25}{4}\right)+\dfrac{15}{4}\right]\left(x^2+5x\right)=0\)
\(\Rightarrow x\left(x+5\right)\left[\left(x+\dfrac{5}{2}\right)^2+\dfrac{15}{4}\right]=0\)
\(\Rightarrow\left[{}\begin{matrix}x=0\\x=-5\\\left(x+\dfrac{5}{2}\right)^2+\dfrac{15}{4}>0\end{matrix}\right.\)