có bạn ạ
\(y^2=5+\sqrt{13+\sqrt{5+\sqrt{13+\sqrt{5+\sqrt{13+...}}}}}\)
\(\Leftrightarrow\left(y^2-5\right)^2=13+y\)
\(\Leftrightarrow y^4-10y^2-y+12=0\Leftrightarrow\left(y-3\right)\left[\left(y+3\right)\left(y+1\right)\left(y-1\right)-1\right]=0\)
do y>2 nen y=3