Question

log(x+2)+log(10x+20)=3

Answer 1

$\log(x+2)+\log(10x+20)=3$
$\log(x+2).(10x+20)=3$
$\log(10x^2+40x+40)=3$
$10x^{2}+40x+40=10^3$
$10x^2+40x+40=1000$
$10x^2+40x+40-1000=0$
$10x^2+40x-960=0$     $(\div 10)$
$x^{2}+4x-96=0$
$(x-8).(x+12)=0$
$x-8=0$     $x+12=0$
$x'=8$       $x"=-12$(não serve)
Portanto,x=8.