How do you solve $log_5 (x+10) + log_5 (x-10) = 3$ ?

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Answer 1 · 2015-12-09T14:43:18

$x in {15}$

$log_5 [(x+10)(x-10)] = log_5 125$

$x^2 - 100 = 125$

$x^2 = 225$

$x = ± 15$

But $x + 10 > 0 and x - 10 > 0$

How do you solve log_5 (x+10) + log_5 (x-10) = 3log_5 (x+10) + log_5 (x-10) = 3?