Bài 1: a, 2x = 16 b, x50 = x
Bài 2: a, x3 = -27 b, (x - 2)2 = 16
1,Tìm x:
a,2x=16 b,x3=27 c,x50=x d,(x - 22)=16
2,So sánh:a,2300 và 3200
b,3500 và 7300
a) \(2^x=16=2^4\Rightarrow x=4\)
b) \(x^3=27=3^3\Rightarrow x=3\)
c) \(x^{50}=x\Rightarrow x\left(x^{49}-1\right)=0\Rightarrow x=0\) hay \(x=1\)
d) \(\left(x-2\right)^2=16=4^2\Rightarrow x-2=4\) hay \(x-2=-4\)
\(\Rightarrow x=6\) hay \(x=-2\)
a) \(2^{300}=2^{3.100}=8^{100}\)
\(3^{200}=3^{2.100}=9^{100}\)
vì \(8^{100}< 9^{100}\)
\(\Rightarrow2^{300}< 3^{200}\)
b) \(3^{500}=3^{5.100}=243^{100}\)
\(7^{300}=7^{3.100}=343^{100}\)
vì \(243^{100}< 343^{100}\)
\(\Rightarrow3^{500}< 7^{300}\)
`@` `\text {Ans}`
`\downarrow`
`1,`
`a,`
`2^x = 16`
`=> 2^x = 2^4`
`=> x = 4`
Vậy, `x = 4`
`b,`
`x^3 = 27`
`=> x^3 = 3^3`
`=> x = 3`
Vậy, `x = 3`
`c,`
\(x^{50}=x\)
`=>`\(x^{50}-x=0\)
`=>`\(x\left(x^{49}-1\right)=0\)
`=>`\(\left[{}\begin{matrix}x=0\\x^{49}-1=0\end{matrix}\right.\)
`=>`\(\left[{}\begin{matrix}x=0\\x^{49}=1\end{matrix}\right.\)
`=>`\(\left[{}\begin{matrix}x=0\\x=1\end{matrix}\right.\)
Vậy, `x \in {0; 1}`
`d,`
`(x-2^2)=16`
`=> x - 2^2 = 16`
`=> x = 16 + 2^2`
`=> x = 20`
Vậy, `x = 20`
`2,`
`a,`
Ta có:
\(2^{300}=\left(2^3\right)^{100}=8^{100}\)
\(3^{200}=\left(3^2\right)^{100}=9^{100}\)
Vì `8 < 9 =>`\(8^{100}< 9^{100}\)
`=>`\(2^{300}< 3^{200}\)
Vậy, \(2^{300}< 3^{200}\)
`b,`
Ta có:
\(3^{500}=\left(3^5\right)^{100}=243^{100}\)
\(7^{300}=\left(7^3\right)^{100}=343^{100}\)
Vì `243 < 343 =>`\(243^{100}< 343^{100}\)
`=>`\(3^{500}< 7^{300}\)
Vậy, \(3^{500}< 7^{300}.\)
a) x3 = 27 b) (2x – 1)3 = 8 c) (x – 2)2 = 16
d) (2x – 3)2 = 9
\(a,\Rightarrow x=3\)
\(b,\Rightarrow2x-1=2\)
\(\Rightarrow2x=3\)
\(\Rightarrow x=\dfrac{3}{2}\)
\(c,\Rightarrow x-2=4\)
\(\Rightarrow x=6\)
\(d,\Rightarrow2x-3=3\)
\(\Rightarrow2x=6\)
\(\Rightarrow x=3\)
Tìm số tự nhiên x, biết
a, x 2 = 16
b, x 3 = 27
c, 2 . x 3 - 4 = 12
d, 5 x 3 - 5 = 0
e, x + 1 2 = 16
f, x + 1 3 = 27
g, x + 1 3 = 16
h, 2 x - 1 7 = x 7
a) x = 4
b) x = 3
c) x = 2
d) x = 1
e) x = 3
f) x = 2
g) x = 4
h) x = 3
a) x3=27, b) (2x-1)3=8,c)(x-2)2=16,d) (2x-3)2=9,e)2x+5=34:32,f)(3x-24.73=2.74
\(a,\Rightarrow x=3\\ b,\Rightarrow2x-1=2\Rightarrow x=\dfrac{3}{2}\\ c,\Rightarrow\left[{}\begin{matrix}x-2=4\\x-2=-4\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=6\\x=-2\end{matrix}\right.\\ d,\Rightarrow\left[{}\begin{matrix}2x-3=3\\2x-3=-3\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=3\\x=0\end{matrix}\right.\\ e,\Rightarrow2x+5=3^2=9\Rightarrow x=2\)
Bài 1: Chứng minh
a. A = 2x ^ 2 + 2x + 1 > 0 với mọi x
b. B = 4 + x ^ 2 + x > 0 với mọi x
Bài 2: Chứng minh
a. A = - x ^ 2 + 3x - 1 < 0 với mọi x
b. B = - 2x ^ 2 - 3x - 3 < 0 với mọi x
Bài 1:
\(a,A=2x^2+2x+1=\left(x^2+2x+1\right)+x^2=\left(x+1\right)^2+x^2\\ Mà:\left(x+1\right)^2\ge0\forall x\in R\\ \Rightarrow\left(x+1\right)^2+x^2>0\forall x\in R\\ Vậy:A>0\forall x\in R\)
2:
a: =-(x^2-3x+1)
=-(x^2-3x+9/4-5/4)
=-(x-3/2)^2+5/4 chưa chắc <0 đâu bạn
b: =-2(x^2+3/2x+3/2)
=-2(x^2+2*x*3/4+9/16+15/16)
=-2(x+3/4)^2-15/8<0 với mọi x
Bài 1:
\(B=4+x^2+x=\left(x^2+x+\dfrac{1}{4}\right)+\dfrac{15}{4}=\left(x+\dfrac{1}{2}\right)^2+\dfrac{15}{4}\ge\dfrac{15}{4}\forall x\in R\\ Vậy:B>0\forall x\in R\)
Bài 1: Giải các phương trình dưới đây
1) x2 - 9 = (x - 3)(5x +2)
2) x3 - 1 = (x - 1)(x2 - 2x +16)
3) 4x2 (x - 1) - x + 1 = 0
4) x3 + 4x2 - 9x - 36 = 0
5) (3x + 5)2 = (x - 1)2
6) 9 (2x + 1)2 = 4 (x - 5)2
7) x2 + 2x = 15
8) x4 + 5x3 + 4x2 = 0
9) (x2 - 4) - (x - 2)(3 - 2x) = 0
10) (3x + 2)(x2 - 1) = (9x2 - 4) (x + 1)
11) (3x - 1)(x2 + 2) = (3x - 1)(7x - 10)
12) (2x2 + 1) (4x - 3) = (x - 12)(2x2 + 1)
1: \(\Leftrightarrow\left(x-3\right)\left(x+3\right)-\left(x-3\right)\left(5x+2\right)=0\)
\(\Leftrightarrow\left(x-3\right)\left(-4x+1\right)=0\)
hay \(x\in\left\{3;\dfrac{1}{4}\right\}\)
2: \(\Leftrightarrow\left(x-1\right)\left(x^2+x+1\right)-\left(x-1\right)\left(x^2-2x+16\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(x^2+x+1-x^2+2x-16\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(3x-15\right)=0\)
hay \(x\in\left\{1;5\right\}\)
3: \(\Leftrightarrow\left(x-1\right)\left(4x^2-1\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(2x-1\right)\left(2x+1\right)=0\)
hay \(x\in\left\{1;\dfrac{1}{2};-\dfrac{1}{2}\right\}\)
4: \(\Leftrightarrow x^2\left(x+4\right)-9\left(x+4\right)=0\)
\(\Leftrightarrow\left(x+4\right)\left(x-3\right)\left(x+3\right)=0\)
hay \(x\in\left\{-4;3;-3\right\}\)
5: \(\Leftrightarrow\left[{}\begin{matrix}3x+5=x-1\\3x+5=1-x\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}2x=-6\\4x=-4\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=-1\end{matrix}\right.\)
6: \(\Leftrightarrow\left(6x+3\right)^2-\left(2x-10\right)^2=0\)
\(\Leftrightarrow\left(6x+3-2x+10\right)\left(6x+3+2x-10\right)=0\)
\(\Leftrightarrow\left(4x+13\right)\left(8x-7\right)=0\)
hay \(x\in\left\{-\dfrac{13}{4};\dfrac{7}{8}\right\}\)
1.
\(\Leftrightarrow\left(x-3\right)\left(x+3\right)=\left(x-3\right)\left(5x-2\right)\)
\(\Leftrightarrow x+3=5x-2\)
\(\Leftrightarrow4x=5\Leftrightarrow x=\dfrac{5}{4}\)
2.
\(\Leftrightarrow\left(x-1\right)\left(x^2+x+1\right)=\left(x-1\right)\left(x^2-2x+16\right)\)
\(\Leftrightarrow x^2+x+1=x^2-2x+16\)
\(\Leftrightarrow3x=15\Leftrightarrow x=5\)
3.
\(\Leftrightarrow4x^2\left(x-1\right)-\left(x-1\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(4x^2-1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=\dfrac{1}{2};x=-\dfrac{1}{2}\end{matrix}\right.\)
7.
\(\Leftrightarrow x^2+2x-15=0\)
\(\Leftrightarrow\left(x-3\right)\left(x+5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=3\\x=-5\end{matrix}\right.\)
8.\(\Leftrightarrow x^4+x^3+4x^3+4x^2=0\)
\(\Leftrightarrow x^3\left(x+1\right)+4x^2\left(x+1\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left(x^3+4x^2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-1\\x=0;x=-4\end{matrix}\right.\)
9.\(\Leftrightarrow\left(x-2\right)\left(x+2\right)=\left(x-2\right)\left(3-2x\right)\)
\(\Leftrightarrow x+2=3-2x\)
\(\Leftrightarrow3x=1\Leftrightarrow x=\dfrac{1}{3}\)
Bài 3: Phân tích các đa thức sau thành nhân tử:
a) x2 + 10x + 25. b) 8x - 16 - x2
c) x3 + 3x2 + 3x + 1 d) (x + y)2 - 9x2
e) (x + 5)2 – (2x -1)2
Bài 4: Tìm x biết
a) x2 – 9 = 0 b) (x – 4)2 – 36 = 0
c) x2 – 10x = -25 d) x2 + 5x + 6 = 0
Bài 3
a) x² + 10x + 25
= x² + 2.x.5 + 5²
= (x + 5)²
b) 8x - 16 - x²
= -(x² - 8x + 16)
= -(x² - 2.x.4 + 4²)
= -(x - 4)²
c) x³ + 3x² + 3x + 1
= x³ + 3.x².1 + 3.x.1² + 1³
= (x + 1)³
d) (x + y)² - 9x²
= (x + y)² - (3x)²
= (x + y - 3x)(x + y + 3x)
= (y - 2x)(4x + y)
e) (x + 5)² - (2x - 1)²
= (x + 5 - 2x + 1)(x + 5 + 2x - 1)
= (6 - x)(3x + 4)
Bài 4
a) x² - 9 = 0
x² = 9
x = 3 hoặc x = -3
b) (x - 4)² - 36 = 0
(x - 4 - 6)(x - 4 + 6) = 0
(x - 10)(x + 2) = 0
x - 10 = 0 hoặc x + 2 = 0
*) x - 10 = 0
x = 10
*) x + 2 = 0
x = -2
Vậy x = -2; x = 10
c) x² - 10x = -25
x² - 10x + 25 = 0
(x - 5)² = 0
x - 5 = 0
x = 5
d) x² + 5x + 6 = 0
x² + 2x + 3x + 6 = 0
(x² + 2x) + (3x + 6) = 0
x(x + 2) + 3(x + 2) = 0
(x + 2)(x + 3) = 0
x + 2 = 0 hoặc x + 3 = 0
*) x + 2 = 0
x = -2
*) x + 3 = 0
x = -3
Vậy x = -3; x = -2
Bài 2 : Phân tích đa thức sau thành nhân tử
a) 5x^2 + 30y
b) x^3 - 2x^2 - 4xy^2 + x
Bài 3 : Tìm x , biết
a) 2x(x - 3 ) - x + 3 = 0
b) ( 3x - 1 ) ( 2x + 1 ) - (x + 1)^2 = 5x^2
Bài 2
a) 5x² + 30y
= 5(x² + 6y)
b) x³ - 2x² - 4xy² + x
= x(x² - 2x - 4y² + 1)
= x[(x² - 2x + 1) - 4y²]
= x[(x - 1)² - (2y)²]
= x(x - 1 - 2y)(x - 1 + 2y)
Bài 3:
a: \(2x\left(x-3\right)-x+3=0\)
=>\(2x\left(x-3\right)-\left(x-3\right)=0\)
=>(x-3)(2x-1)=0
=>\(\left[{}\begin{matrix}x-3=0\\2x-1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=\dfrac{1}{2}\end{matrix}\right.\)
b: \(\left(3x-1\right)\left(2x+1\right)-\left(x+1\right)^2=5x^2\)
=>\(6x^2+3x-2x-1-x^2-2x-1=5x^2\)
=>\(5x^2-x-2=5x^2\)
=>-x-2=0
=>-x=2
=>x=-2
Tìm số tự nhiên x, biết
a) x 2 = 16
b) x 3 = 27
c) 2 . x 3 - 4 = 12
d) 5 . x 3 - 5 = 0