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heureka

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 #4
avatar+26396 
+5

...continued.

if x is in degrees:

\\cos(x) = cos\left[180\textcolor[rgb]{1,0,0}{\ensuremath{^\circ}}-cos^{-1}(\frac{0.25}{6,76}*\cos{(x)})\right]  \quad | \quad \pm cos^{-1}\\  \pm x=\pm \left[ 180\ensuremath{^\circ}} -cos^{-1}(\frac{0.25}{6,76}*\cos{(x)})\right]\\  x=180\ensuremath{^\circ}} -cos^{-1}(\frac{0.25}{6,76}*\cos{(x)})\\  cos^{-1}(\frac{0.25}{6,76}*\cos{(x)})\right]=180\ensuremath{^\circ}}-x  \quad | \quad \cos{}\\\\  \frac{0.25}{6,76}*\cos{(x)}=\cos{(180\ensuremath{^\circ}}-x)}\\  \frac{0.25}{6,76}*\cos{(x)}=\underbrace{\cos{180\ensuremath{^\circ}}}_{-1}\cos{(x)}  +\underbrace{\sin{180\ensuremath{^\circ}}}_{0}\sin{(x)}\\  \frac{0.25}{6,76}*\cos{(x)}=-\cos{(x)}\\  \frac{0.25}{6,76}*\cos{(x)}+\cos{(x)}=0\\  \cos{(x)}\left(\frac{0.25}{6,76}+1\right)=0\\  \cos{(x)}=0\quad | \quad \pm \cos^{-1}\\  \pm x=\frac{\pi}{2}\\\\  \boxed{x=\frac{\pi}{2} \pm 2\pi*k\qquad or \qquad x=-\frac{\pi}{2} \pm 2\pi*k}

\\cos(x) = cos\left[180\textcolor[rgb]{1,0,0}{\ensuremath{^\circ}}-cos^{-1}(\frac{0.25}{6,76}*\cos{(x)})\right]
\quad | \quad \pm cos^{-1}\\
\pm x=\pm \left[ 180\ensuremath{^\circ}} -cos^{-1}(\frac{0.25}{6,76}*\cos{(x)})\right]\\
x=180\ensuremath{^\circ}} -cos^{-1}(\frac{0.25}{6,76}*\cos{(x)})\\
cos^{-1}(\frac{0.25}{6,76}*\cos{(x)})\right]=180\ensuremath{^\circ}}-x
\quad | \quad \cos{}\\\\
\frac{0.25}{6,76}*\cos{(x)}=\cos{(180\ensuremath{^\circ}}-x)}\\
\frac{0.25}{6,76}*\cos{(x)}=\underbrace{\cos{180\ensuremath{^\circ}}}_{-1}\cos{(x)}
+\underbrace{\sin{180\ensuremath{^\circ}}}_{0}\sin{(x)}\\
\frac{0.25}{6,76}*\cos{(x)}=-\cos{(x)}\\
\frac{0.25}{6,76}*\cos{(x)}+\cos{(x)}=0\\
\cos{(x)}\left(\frac{0.25}{6,76}+1\right)=0\\
\cos{(x)}=0\quad | \quad  \pm \cos^{-1}\\
\pm x=\frac{\pi}{2}\\\\
\boxed{x=\frac{\pi}{2} \pm 2\pi*k\qquad or \qquad x=-\frac{\pi}{2} \pm 2\pi*k}




May 16, 2014
 #8
avatar+26396 
+5

1.) See "Vieta"

2.) You find x1=1 do:

\begin{array}{  rlllr  } (   x^3  &  +4x^2  &  +x  &   -6)  &  :  (x-1)  =\textcolor[rgb]{1,0,0}{x^2}\textcolor[rgb]{0,0,1}{+5x}\textcolor[rgb]{0,1,0}{+6}  \\  \textcolor[rgb]{1,0,0}{{\underline{-(  x^3}}  &  \textcolor[rgb]{1,0,0}{\underline{-x^2)}}}  &  &  &  \\  0  &  +5x^2  &  +x  \\  &  \textcolor[rgb]{0,0,1}{\underline{-(5x^2}}  &  \textcolor[rgb]{0,0,1}{\underline{-5x)}}  \\  &  0  &  +6x  &  -6  \\  &&  \textcolor[rgb]{0,1,0}{\underline{-(6x}}  &  \textcolor[rgb]{0,1,0}{\underline{-6)}}  \\  &&  0  &  +0  \end{array}

\begin{array}{
rlllr
} (
x^3
&
+4x^2
&
+x
&
-6)
&
:
(x-1)
=\textcolor[rgb]{1,0,0}{x^2}\textcolor[rgb]{0,0,1}{+5x}\textcolor[rgb]{0,1,0}{+6}
\\
\textcolor[rgb]{1,0,0}{{\underline{-(
x^3}}
&
\textcolor[rgb]{1,0,0}{\underline{-x^2)}}}
&
&
&
\\
0
&
+5x^2
&
+x
\\
&
\textcolor[rgb]{0,0,1}{\underline{-(5x^2}}
&
\textcolor[rgb]{0,0,1}{\underline{-5x)}}
\\
&
0
&
+6x
&
-6
\\
&&
\textcolor[rgb]{0,1,0}{\underline{-(6x}}
&
\textcolor[rgb]{0,1,0}{\underline{-6)}}
\\
&&
0
&
+0
\end{array}

so we have: x3+4x2+x6=(x1)(x2+5x+6)

x^3+4x^2+x-6=(x-1)(x^2+5x+6)

We solve:

x2+5x+6=0x2+5x+(52)2(52)2+6=0(x+52)2=2546(x+52)2=14|±x+52=±14x2,3=52±12x2=52+12=42=2_x3=5212=62=3_

\\x^2+5x+6=0\\
x^2+5x+(\textcolor[rgb]{1,0,0}{\frac{5}{2}})^2-(\textcolor[rgb]{1,0,0}{\frac{5}{2}})^2+6=0\\
\left( x+\frac{5}{2}\right)^2=\frac{25}{4}-6\\
\left( x+\frac{5}{2}\right)^2=\frac{1}{4}\qquad| \quad \pm\sqrt{}\\
x+\frac{5}{2}=\pm\sqrt{\frac{1}{4}}\\
x_{2,3}=-\frac{5}{2}\pm\frac{1}{2}\\
x_2=-\frac{5}{2}+\frac{1}{2}=-\frac{4}{2}=\underline{-2}\\
x_3=-\frac{5}{2}-\frac{1}{2}=-\frac{6}{2}=\underline{-3}\\

x1=1x2=2x3=3x3+4x2+x6=(x1)(x+2)(x+3)

\\x_1=1 \qquad x_2=-2 \qquad x_3=-3\\
\boxed{x^3+4x^2+x-6=(x-1)(x+2)(x+3)}

 
May 15, 2014
 #6
avatar+26396 
+5

1.) See "Vieta"

2.) You find x1=1 do:

\begin{array}{  rlllr  } (   x^3  &  +4x^2  &  +x  &   -6)  &  :  (x-1)  =\textcolor[rgb]{1,0,0}{x^2}\textcolor[rgb]{0,0,1}{+5x}\textcolor[rgb]{0,1,0}{+6}  \\  \textcolor[rgb]{1,0,0}{{\underline{-(  x^3}}  &  \textcolor[rgb]{1,0,0}{\underline{-x^2)}}}  &  &  &  \\  0  &  +5x^2  &  +x  \\  &  \textcolor[rgb]{0,0,1}{\underline{-(5x^2}}  &  \textcolor[rgb]{0,0,1}{\underline{-5x)}}  \\  &  0  &  +6x  &  -6  \\  &&  \textcolor[rgb]{0,1,0}{\underline{-(6x}}  &  \textcolor[rgb]{0,1,0}{\underline{-6)}}  \\  &&  0  &  +0  \end{array}

so we have: x3+4x2+x6=(x1)(x2+5x+6)

We solve:

x2+5x+6=0x2+5x+(52)2(52)2+6=0(x+52)2=2546(x+52)2=14|±x+52=±14x2,3=52±12x2=52+12=42=2_x3=5212=62=3_

x1=1x2=2x3=3x3+4x2+x6=(x1)(x+2)(x+3)

.
May 15, 2014