cevap ;$\left( 11\right) _{a}$
http://matkafasi.com/14067/3ten-buyuk-sayi-tabani-sqrt-left-right-ifadesinin-esiti-nedir?show=14067#q14067
sorusuna bakabilirsin.
$\sqrt[4]{a^4+4a^3+6a^2+4a+1}=\sqrt[4]{(a+1)^4}=(a+1)_{10}$