Question

Решить уравнение log (127+x³)-3log(x+1)=0

Answer 1

Log(127+x³)-3*log(x+1)=0
ОДЗ:
$\left \{ {{127+ x^{3} \ \textgreater \ 0} \atop {x+1\ \textgreater \ 0}} \right. , \left \{ {{ x^{3}\ \textgreater \ -127 } \atop {x\ \textgreater \ -1}} \right. , \left \{ {{x\ \textgreater \ \sqrt[3]{-127} } \atop {x\ \textgreater \ -1}} \right.$
x>-1. x∈(-1;∞)
log(127+x³)=3*log(x+1)
log(127+x³)=log(x+1)³
127+x³=(x+1)³
127+x³=x³+3x²+3x+1
3x²+3x-126=0 |:3
x²+x-42=0
D=169
x₁=-7, x₂=6
-7∉(-1;∞). => x=-7 посторонний корень

ответ: x=6