5 log (x+5) + 5 log (x-3) - 5 log (x+15) = 0

5'log (x + 5) + 5'log (x - 3) - 5'log (x + 15) = 0
5'log ((x + 5)(x - 3)/(x + 15)) = 5'log 1
(x + 5)(x - 3)/(x + 15) = 1
x² + 2x - 15 = x + 15
x² + x - 30 = 0
(x + 6)(x - 5) = 0
x = -6 ; x = 5

NiLai x yg memenuhi :
x = 5