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x²-2x- 8 = 0 solve by factorising quadratic equation

 Feb 16, 2015

Best Answer 

 #2
avatar+26376 
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x²-2x- 8 = 0 solve by factorising quadratic equation

$$\\(-2)*(+4) = -8 \\
(-2) +4 = 2\\
\boxed{(x-4)(x+2) = x^2-2x-8=0 } \\
x_1 = -2\\
x_2 = 4$$

 Feb 16, 2015
 #1
avatar+8 
+5

$${\left({\mathtt{x}}{\mathtt{\,-\,}}{\mathtt{1}}\right)}^{{\mathtt{2}}} = {{\mathtt{x}}}^{{\mathtt{2}}}{\mathtt{\,-\,}}{\mathtt{2}}{\mathtt{\,\times\,}}{\mathtt{x}}{\mathtt{\,\small\textbf+\,}}{\mathtt{1}}$$

if you write your equation as this:$${\left({\mathtt{x}}{\mathtt{\,-\,}}{\mathtt{1}}\right)}^{{\mathtt{2}}}{\mathtt{\,-\,}}{\mathtt{9}}$$

you can use this rule:$${{\mathtt{a}}}^{{\mathtt{2}}}{\mathtt{\,-\,}}{{\mathtt{b}}}^{{\mathtt{2}}} = \left({\mathtt{a}}{\mathtt{\,-\,}}{\mathtt{b}}\right){\mathtt{\,\times\,}}\left({\mathtt{a}}{\mathtt{\,\small\textbf+\,}}{\mathtt{b}}\right)$$

finally you can write your  equation as:$$\left(\left({\mathtt{x}}{\mathtt{\,-\,}}{\mathtt{4}}\right){\mathtt{\,\times\,}}\left({\mathtt{x}}{\mathtt{\,\small\textbf+\,}}{\mathtt{2}}\right)\right)$$

so this means: 4 and -2 are your solutions. I hope I could explain

 Feb 16, 2015
 #2
avatar+26376 
+5
Best Answer

x²-2x- 8 = 0 solve by factorising quadratic equation

$$\\(-2)*(+4) = -8 \\
(-2) +4 = 2\\
\boxed{(x-4)(x+2) = x^2-2x-8=0 } \\
x_1 = -2\\
x_2 = 4$$

heureka Feb 16, 2015

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