BdMO National Junior 2007/4
Posted: Sun Feb 24, 2019 8:59 am
If $log_{(x+3)}(x^2+15)=2$ then $x=?$
Answer:$\fbox 1$
Solution:
\[log_{(x+3)}(x^2+15)=2\]
\[\Rightarrow (x+3)^2=x^2+15\]
\[\Rightarrow x^2+6x+9=x^2+15\]
\[\Rightarrow 6x=15-9\]
\[\Rightarrow 6x=6\]
\[\Rightarrow x=1\]