1.
a) x^2+36
b) 9x^2-4
c) x^3+64
d) 8x^3+27
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31 tháng 7 2023
a: x^3=7^3
=>x^3=343
=>\(x=\sqrt[3]{343}=7\)
b: x^3=27
=>x^3=3^3
=>x=3
c: x^3=125
=>x^3=5^3
=>x=5
d: (x+1)^3=125
=>x+1=5
=>x=4
e: (x-2)^3=2^3
=>x-2=2
=>x=4
f: (x-2)^3=8
=>x-2=2
=>x=4
h: (x+2)^2=64
=>x+2=8 hoặc x+2=-8
=>x=6 hoặc x=-10
j: =>x-3=2 hoặc x-3=-2
=>x=1 hoặc x=5
k:
9x^2=36
=>x^2=36/9
=>x^2=4
=>x=2 hoặc x=-2
l:
(x-1)^4=16
=>(x-1)^2=4(nhận) hoặc (x-1)^2=-4(loại)
=>x-1=2 hoặc x-1=-2
=>x=3 hoặc x=-1
4 tháng 10 2021
1) \(\dfrac{1}{27}+a^3=\left(\dfrac{1}{3}+a\right)\left(\dfrac{1}{9}-\dfrac{a}{3}+a^2\right)\)
2) \(=\left(2x+3y\right)\left(4x^2-6xy+9y^2\right)\)
3) \(=\left(\dfrac{1}{2}x+2y\right)\left(\dfrac{1}{4}x-xy+4y^2\right)\)
4) \(=\left(x^2+1\right)\left(x^4-x^2+1\right)\)
5) \(=\left(x^3+1\right)\left(x^6-x^3+1\right)\)
6) \(=\left(x-4\right)\left(x^2+4x+16\right)\)
7) \(=\left(x-5\right)\left(x^2+5x+25\right)\)
8) \(=\left(2x^2-3y\right)\left(4x^4+6x^2y+9y^2\right)\)
9) \(=\left(\dfrac{1}{4}x^2-5y\right)\left(\dfrac{1}{16}x^4+\dfrac{5}{4}x^2y+25y^2\right)\)
10) \(=\left(\dfrac{1}{2}x-2\right)\left(\dfrac{1}{4}x^2+x+4\right)\)
11) \(=\left(x+2\right)^3\)
12) \(=\left(x+3\right)^3\)
22 tháng 10 2018
1. a) \(8x^3-32x=8x\left(x^2-4\right)=8x\left(x-4\right)\left(x+4\right)\)
b) \(y^3+64+\left(y+4\right)\left(y-16\right)=\left(y^3+4^3\right)+\left(y+4\right)\left(y-16\right)\)
\(=\left(y+4\right)\left(y^2-4y+16\right)+\left(y+4\right)\left(y-16\right)=\left(y+4\right)\left(y^2-4y+16+y-16\right)\)
\(=\left(y-4\right)\left(y^2-3y\right)=\left(y-4\right)y\left(y-3\right)\)
2) a)
\(4x^3-9x=0\)
\(\Leftrightarrow x\left(4x^2-9\right)=0\)
\(\Leftrightarrow x\left(2x+3\right)\left(2x-3\right)=0\)
<=> x=0 hoặc 2x+3=0 hoặc 2x-3=0
<=> x=0 hoặc x=-3/2 hoặc x=3/2
b) \(A=x^3-9x^2+27x-27=x^3-3.x^2.3+3.x.3^2-3^3=\left(x-3\right)^3\)
Tại x=203
A=(203-3)3=2003
22 tháng 10 2018
Bài 1 :
a) \(8x^3-32x\)
\(=8x\left(x^2-4\right)\)
\(=8x\left(x-2\right)\left(x+2\right)\)
b) \(y^3+64+\left(y+4\right)\left(y-16\right)\)
\(=\left(y^3+4^3\right)+\left(y+4\right)\left(y-16\right)\)
\(=\left(y+4\right)\left(y^2-4y+16\right)+\left(y+4\right)\left(y-16\right)\)
\(=\left(y+4\right)\left(y^2-4x+16+y-16\right)\)
\(=\left(y+4\right)\left(y^2+y-4x\right)\)
Bài 2 :
a) \(4x^3-9x=0\)
\(x\left(4x^2-9\right)=0\)
\(x\left[\left(2x\right)^2-3^2\right]=0\)
\(x\left(2x-3\right)\left(2x+3\right)=0\)
\(\Rightarrow\hept{\begin{cases}x=0\\2x-3=0\\2x+3=0\end{cases}\Rightarrow\hept{\begin{cases}x=0\\x=\frac{3}{2}\\x=\frac{-3}{2}\end{cases}}}\)
P.s: ở trên dùng ngoặc vuông nhé
b) \(A=x^3-9x^2+27x-27\)
\(A=x^3-3\cdot x^2\cdot3+3\cdot x\cdot3^2-3^3\)
\(A=\left(x-3\right)^3\)
Thay x = 203 vào biểu thức ta có :
\(A=\left(203-3\right)^3\)
\(A=200^3\)
\(A=8000000\)
S
6 tháng 10 2018
\(a.x^3-6x=x^3-4^3=\left(x-4\right)\left(x^2+4x+16\right)\)
\(b.x^4+6x^3+11x^2+6x+1=x^4+6x^3+9x^2+2x^2+6x+1\)
\(=\left(x^2+3x+1\right)^2\)
\(c.x^2+3x+2=x^2+x+2x+2=x\left(x+1\right)+2\left(x+1\right)=\left(x+1\right)\left(x+2\right)\)
\(d.x\left(x+1\right)\left(x+2\right)\left(x+3\right)+1\)
\(=x\left(x+3\right)\left(x+1\right)\left(x+2\right)+1=\left(x^2+3x\right)\left(x^2+3x+2\right)+1\)
Đặt \(x^2+3x=y\Rightarrow y\left(y+2\right)+1=y^2+2y+1=\left(y+1\right)^2\)
Thay \(y=x^2+3x\) ta được: \(\left(y+1\right)^2=\left(x^2+3x+1\right)^2\)
\(e.x^3+9x^2+27x+27=\left(x+3\right)^3\)
\(f.\left(x+1\right)\left(x+7\right)\left(x^2+8x+15\right)+15=\left(x^2+8x+7\right)\left(x^2+8x+15\right)+15\)
Đặt \(a=x^2+8x+11\Rightarrow\left(a-4\right)\left(a+4\right)+15=a^2-16+15=a^2-1=\left(a+1\right)\left(a-1\right)\)
Thay \(a=x^2+8x+11\) ta được: \(\left(a+1\right)\left(a-1\right)=\left(x^2+8x+12\right)\left(x^2+8x+10\right)\)
22 tháng 10 2021
\(a,=x^2-4x+4-\dfrac{15}{4}=\left(x-2\right)^2-\dfrac{15}{4}=\left(x-2-\dfrac{\sqrt{15}}{2}\right)\left(x-2+\dfrac{\sqrt{15}}{2}\right)\\ b,=?\\ c,\Rightarrow x^2+7x-8=0\\ \Rightarrow\left(x+8\right)\left(x-1\right)=0\Rightarrow\left[{}\begin{matrix}x=-8\\x=1\end{matrix}\right.\\ d,Sửa:x^3-3x^2=-27+9x\\ \Rightarrow x^3-3x^2+9x-27=0\\ \Rightarrow x^2\left(x-3\right)+9\left(x-3\right)=0\\ \Rightarrow\left(x^2+9\right)\left(x-3\right)=0\Rightarrow\left[{}\begin{matrix}x^2=-9\left(vô.lí\right)\\x=3\end{matrix}\right.\\ \Rightarrow x=3\\ e,\Rightarrow x\left(x-3\right)-7x+21=0\\ \Rightarrow x\left(x-3\right)-7\left(x-3\right)=0\\ \Rightarrow\left(x-7\right)\left(x-3\right)=0\Rightarrow\left[{}\begin{matrix}x=7\\x=3\end{matrix}\right.\\ f,\Rightarrow x^2\left(x-2\right)+\left(x-2\right)=0\\ \Rightarrow\left(x^2+1\right)\left(x-2\right)=0\Rightarrow\left[{}\begin{matrix}x^2=-1\left(vô.lí\right)\\x=2\end{matrix}\right.\\ \Rightarrow x=2\)
\(g,\Rightarrow x^2-4x+4=0\\ \Rightarrow\left(x-2\right)^2=0\\ \Rightarrow x=2\\ h,Sửa:x^3-x^2+x=1\\ \Rightarrow x^2\left(x-1\right)+\left(x-1\right)=0\\ \Rightarrow\left(x^2+1\right)\left(x-1\right)=0\Rightarrow\left[{}\begin{matrix}x^2=-1\left(vô.lí\right)\\x=1\end{matrix}\right.\\ \Rightarrow x=1\)
16 tháng 10 2020
Bài 1: Tìm x
a) Ta có: \(\left(2x+1\right)^2-4\left(x+2\right)^2=9\)
\(\Leftrightarrow4x^2+4x+1-4\left(x^2+4x+4\right)-9=0\)
\(\Leftrightarrow4x^2+4x+1-4x^2-16x-16-9=0\)
\(\Leftrightarrow-12x-24=0\)
\(\Leftrightarrow-12x=24\)
hay x=-2
Vậy: x=-2
b) Ta có: \(\left(3x-1\right)^2+2\left(x+3\right)^2+11\left(x+1\right)\left(1-x\right)=6\)
\(\Leftrightarrow9x^2-6x+1+2\left(x^2+6x+9\right)-11\left(x-1\right)\left(x+1\right)-6=0\)
\(\Leftrightarrow9x^2-6x+1+2x^2+12x+18-11\left(x^2-1\right)-6=0\)
\(\Leftrightarrow11x^2+6x+12-11x^2+11=0\)
\(\Leftrightarrow6x+23=0\)
\(\Leftrightarrow6x=-23\)
hay \(x=-\frac{23}{6}\)
Vậy: \(x=-\frac{23}{6}\)
c) Ta có: \(8x^3-12x^2+6x-1=0\)
\(\Leftrightarrow\left(2x\right)^3-3\cdot\left(2x\right)^2\cdot1+3\cdot2x\cdot1^2-1^3=0\)
\(\Leftrightarrow\left(2x-1\right)^3=0\)
\(\Leftrightarrow2x-1=0\)
\(\Leftrightarrow2x=1\)
hay \(x=\frac{1}{2}\)
Vậy: \(x=\frac{1}{2}\)
d) Ta có: \(x^3+9x^2+27x+27=0\)
\(\Leftrightarrow x^3+3\cdot x^2\cdot3+3\cdot x\cdot3^2+3^3=0\)
\(\Leftrightarrow\left(x+3\right)^3=0\)
\(\Leftrightarrow x+3=0\)
hay x=-3
Vậy: x=-3
KV
16 tháng 10 2020
a) (2x + 1)2 - 4(x + 2)2 = 9
4x2 + 4x + 1 - 4(x2 + 4x + 4) = 9
4x2 + 4x + 1 - 4x2 - 16x - 16 = 9
-12x - 15 = 9
-12x = 9 + 15
-12x = 24
x = 12 : (-2)
x = -2
b) (3x - 1)2 + 2(x + 3)2 + 11(x + 1)(1 - x) = 6
9x2 - 6x + 1 + 2(x2 + 6x + 9) - 11(x + 1)(x - 1) = 6
9x2 - 6x + 1 + 2x2 + 12x + 18 - 11(x2 - 1) = 6
9x2 - 6x + 1 + 2x2 + 12x + 18 - 11x2 + 11 = 6
6x + 30 = 6
6x = 6 - 30
6x = -24
x = -24 : 6
x = -4
c) 8x3 - 12x2 + 6x - 1 = 0
(2x)3 - 3.(2x)2.1 + 3.2x.12 - 13 = 0
(2x - 1)3 = 0
2x - 1 = 0
2x = 1
x = 1/2
d) x3 + 9x2 + 27x + 27 = 0
x3 + 3.x2.3 + 3.x.32 + 33 = 0
(x + 3)3 = 0
x + 3 = 0
x = 0 - 3
x = -3
19 tháng 6 2021
a, 4x2 - 49 = 0
⇔⇔ (2x)2 - 72 = 0
⇔⇔ (2x - 7)(2x + 7) = 0
⇔{2x−7=02x+7=0⇔⎧⎪ ⎪⎨⎪ ⎪⎩x=72x=−72⇔{2x−7=02x+7=0⇔{x=72x=−72
b, x2 + 36 = 12x
⇔⇔ x2 + 36 - 12x = 0
⇔⇔ x2 - 2.x.6 + 62 = 0
⇔⇔ (x - 6)2 = 0
⇔⇔ x = 6
19 tháng 6 2021
e, (x - 2)2 - 16 = 0
⇔⇔ (x - 2)2 - 42 = 0
⇔⇔ (x - 2 - 4)(x - 2 + 4) = 0
⇔⇔ (x - 6)(x + 2) = 0
⇔{x−6=0x+2=0⇔{x=6x=−2⇔{x−6=0x+2=0⇔{x=6x=−2
f, x2 - 5x -14 = 0
⇔⇔ x2 + 2x - 7x -14 = 0
⇔⇔ x(x + 2) - 7(x + 2) = 0
⇔⇔ (x + 2)(x - 7) = 0
⇔{x+2=0x−7=0⇔{x=−2x=7
D là câu gì
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