8x³ - 4x² + 2x - 1 = 0

<=> ( 8x³ - 4x² ) + ( 2x - 1 ) = 0

<=> 4x²( 2x - 1 ) + ( 2x - 1 ) = 0

<=> ( 2x - 1 )( 4x² + 1 ) = 0

<=> \(\orbr{\begin{cases}2x-1=0\\4x^2+1=0\end{cases}}\Leftrightarrow x=\frac{1}{2}\) ( do 4x² + 1 ≥ 1 > 0 ∀ x )

\(8x^3-4x^2+2x-1=0\)

\(\left(8x^3-4x^2\right)+\left(2x-1\right)=0\)

\(4x^2\left(2x-1\right)+\left(2x-1\right)=0\)

\(\left(2x-1\right)\left(4x^2+1\right)=0\)

\(\Rightarrow\orbr{\begin{cases}2x-1=0\\4x^2+1=0\end{cases}\Rightarrow x=\frac{1}{2}}\)

Đề bài??

đề bải là j bạn quên rồi kìa

Ta có: \(\left(a+b+c\right)^2=a^2+b^2+c^2\)

\(\Leftrightarrow a^2+b^2+c^2+2\left(ab+bc+ca\right)=a^2+b^2+c^2\)

\(\Leftrightarrow ab+bc+ca=0\)

\(\Rightarrow\hept{\begin{cases}ab=-bc-ca\\bc=-ca-ab\\ca=-ab-bc\end{cases}}\)

Thay vào ta được: \(\frac{a^2}{a^2+2bc}=\frac{a^2}{a^2+bc-ca-ab}=\frac{a^2}{\left(a-b\right)\left(a-c\right)}\)

Tương tự: \(\frac{b^2}{b^2+2ca}=\frac{b^2}{\left(b-a\right)\left(b-c\right)}\) ; \(\frac{c^2}{c^2+2ab}=\frac{c^2}{\left(c-a\right)\left(c-b\right)}\)

\(\Rightarrow P=-\left[\frac{a^2}{\left(a-b\right)\left(c-a\right)}+\frac{b^2}{\left(b-c\right)\left(a-b\right)}+\frac{c^2}{\left(c-a\right)\left(b-c\right)}\right]\)

\(=-\left[\frac{a^2\left(b-c\right)+b^2\left(c-a\right)+c^2\left(a-b\right)}{\left(a-b\right)\left(b-c\right)\left(c-a\right)}\right]\)

\(=\frac{\left(b-c\right)\left(a^2+bc-ca-ab\right)}{\left(a-b\right)\left(b-c\right)\left(a-c\right)}\)

\(=\frac{\left(b-c\right)\left(a-b\right)\left(a-c\right)}{\left(a-b\right)\left(b-c\right)\left(a-c\right)}=1\)

\(\left(a+b+c\right)^2=a^2+b^2+c^2\Leftrightarrow ab+ac+bc=0\)

\(\frac{a^2}{a^2+2bc}=\frac{a^2}{a^2-ab-ac+bc}=\frac{a^2}{\left(a-b\right)\left(a-c\right)}\)

Tương tự: \(\frac{b^2}{b^2+2ac}=\frac{b^2}{\left(b-a\right)\left(b-c\right)};\frac{c^2}{c^2+2ac}=\frac{c^2}{\left(c-a\right)\left(c-b\right)}\)

\(P=\frac{a^2}{a^2+2bc}+\frac{b^2}{b^2+2ac}+\frac{c^2}{c^2+2ab}\)

\(=\frac{a^2}{\left(a-b\right)\left(a-c\right)}-\frac{b^2}{\left(a-b\right)\left(b-c\right)}+\frac{c^2}{\left(a-c\right)\left(b-c\right)}\)\(=\frac{\left(a-b\right)\left(a-c\right)\left(b-c\right)}{\left(a-b\right)\left(a-c\right)\left(b-c\right)}=1\)

Dễ mà :

\(4x^2+6x\)

\(=2x\left(2x+3\right)\)

Học tốt

Ta có: \(\frac{1}{x}+\frac{1}{y}+\frac{1}{z}=\frac{1}{x+y+z}\)

\(\Leftrightarrow\frac{xy+yz+zx}{xyz}=\frac{1}{x+y+z}\)

\(\Leftrightarrow\left(xy+yz+zx\right)\left(x+y+z\right)=xyz\)

\(\Leftrightarrow x^2y+xy^2+y^2z+yz^2+z^2x+zx^2+3xyz-xyz=0\)

\(\Leftrightarrow\left(x^2y+xy^2\right)+\left(yz^2+z^2x\right)+\left(zx^2+2xyz+y^2z\right)=0\)

\(\Leftrightarrow xy\left(x+y\right)+z^2\left(x+y\right)+z\left(x+y\right)^2=0\)

\(\Leftrightarrow\left(x+y\right)\left(xy+z^2+yz+zx\right)=0\)

\(\Leftrightarrow\left(x+y\right)\left(y+z\right)\left(z+x\right)=0\)

=> x = -y hoặc y = -z hoặc z = -x

Không mất tổng quát giả sử x = -y, khi đó:

\(\frac{1}{x^{2015}}+\frac{1}{y^{2015}}+\frac{1}{z^{2015}}=-\frac{1}{y^{2015}}+\frac{1}{y^{2015}}+\frac{1}{z^{2015}}=\frac{1}{z^{2015}}\)

\(\frac{1}{x^{2015}+y^{2015}+z^{2015}}=\frac{1}{-y^{2015}+y^{2015}+z^{2015}}=\frac{1}{z^{2015}}\)

\(\Rightarrow\frac{1}{x^{2015}}+\frac{1}{y^{2015}}+\frac{1}{z^{2015}}=\frac{1}{x^{2015}+y^{2015}+z^{2015}}\)

AD=ED 

Định lí Talet đảo: \(\frac{AD}{AB}=\frac{AE}{AC}\Rightarrow DE//BC\)

Mà \(AH\perp BC\)nên \(AH\perp DE\)

Mà \(\Delta ADE\)cân tại \(A\)nên \(AH\)cũng là đường trung trực của \(DE\)

\(\Rightarrow D,E\)đối xứng nhau qua \(AH\)

Theo đề bài: \(a+b+c=0\Rightarrow a=-\left(b+c\right)\Rightarrow a^2=\text{[}-\left(b+c\right)^2\text{]}\)

do đó \(a^2=b^2+c^2+2bc\Rightarrow a^2-b^2-c^2=2bc\left(1\right)\)

Bình phương 2 về của (1) ta được:

\(a^4+b^4+c^4=2a^2b^2-2a^2c^2+2b^2c^2=4b^2c^2\)

\(\Rightarrow a^4+b^4+c^4=2a^2b^2+2a^2c^2+2b^2c^2\)

\(\Rightarrow2\left(a^4+b^4+c^4\right)==\left(a^2+b^2+c^2\right)^2\)

Vì \(a^2+b^2+c^2=1\Rightarrow2\left(a^4+b^4+c^4\right)=1\Rightarrow a^4+b^4+c^4=\frac{1}{2}\)

a)  n_SO3 = \(\frac{3}{80}\) = 0,0375 (mol)

P/ứ : SO₃   + H₂O   -----> H₂SO₄           (1)

Theo pứ (1) : n_H2SO4  = n_SO3 = 0,0375 (mol)

=> Khối lượng H2SO4 có trong dung dịch sau phản ứng là : 

      0,0375  .   98 = 3,675 (g)

b) P/ứ :  Zn    +  H₂SO₄    ----->  ZnSO₄   + H₂     (2)

Theo pứ (2) : n_Zn  =  n_H2SO4 = 0,0375 (mol)

=> Khối lượng Zn phản ứng là : 0,0375  . 65 = 2,4375 (g) = M

Vậy M = 2,4375

5x² = 2 + 3x

<=> 5x² - 3x - 2 = 0

<=> 5x² - 5x + 2x - 2 = 0

<=> 5x( x - 1 ) + 2( x - 1 ) = 0

<=> ( x - 1 )( 5x + 2 ) = 0

<=> x - 1 = 0 hoặc 5x + 2 = 0

<=> x = 1 hoặc x = -2/5

\(5x^2=2+3x\Leftrightarrow5x^2-3x-2=0\Leftrightarrow\left(5x+2\right)\left(x-1\right)=0\Leftrightarrow\orbr{\begin{cases}x=-\frac{2}{5}\\x=1\end{cases}}\)