若k进制123（k）与二进制100110（2）相等,则k=?

123(k)=1*k^2+2*k+3=k^2+2*k+3
100110(2)=1*2^5+1*2^2+1*2=2^5+2^2+2=38
k^2+2*k+3=38
k^2+2*k-35=0
(k+7)*(k-5)=0
k1=-7
k2=5
k=5
123(5)=100110(2)