2^log10(x)-(1/4)*x^log10(4)=0　⇔　4=x^log10(4)/2^log10(x)、また
x^log10(4)=x^{log2(4)/log2(10)}、2^log10(x)={2^log2(x)}^(1/log2(10)}=x^(1/log2(10)} より、
x^log10(4)/2^log10(x)=x^{(log2(4)-1}/log2(10)}=x^{1/log2(10)}=4
⇔　x=4^{log2(10)}=4^{log4(10)/log4(2)}=10^{1/log4(2)}=10^2