Nog een voorbeeld
$
\eqalign{
& \sqrt {11 - x} - \sqrt {x + 6} = 3 \cr
& \left( {\sqrt {11 - x} - \sqrt {x + 6} } \right)^2 = 9 \cr
& 11 - x - 2\sqrt {11 - x} \cdot \sqrt {x + 6} + x + 6 = 9 \cr
& 2\sqrt {\left( {11 - x} \right)\left( {x + 6} \right)} = 8 \cr
& \sqrt {\left( {11 - x} \right)\left( {x + 6} \right)} = 4 \cr
& \left( {11 - x} \right)\left( {x + 6} \right) = 16 \cr
& 11x + 66 - x^2 - 6x = 16 \cr
& - x^2 + 5x + 66 = 16 \cr
& - x^2 + 5x + 50 = 0 \cr
& x^2 - 5x - 50 = 0 \cr
& (x - 10)(x + 5) = 0 \cr
& x = 10\,\,\,(v.n.)\,\,\, \vee x = - 5 \cr
& x = - 5 \cr
& {\text{controle}} \cr
& \sqrt {11 - - 5} - \sqrt { - 5 + 6} = 3 \cr
& \sqrt {16} - \sqrt 1 = 3 \cr
& 4 - 1 = 3 \cr
& {\text{klopt!}} \cr}
$
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