Work Step by Step
$x^2-k^2=0$ $x^2+xk-xk-k^2=0$ $x(x+k)-k(x+k) =0$ $(x-k)(x+k) = 0$ $x-k =0$ $x-k+k = 0+k$ $x = k$ $x+k =0$ $x+k-k = 0-k$ $x = -k$
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