设所求量为x.2^x=12.两边取以2为低的对数,得到x=log(2)12=log(2)(3*4)=log(2)3+log(2)(2^2)=log(2)3+2.用计算器可以算得log(2)3=lg3/lg2≈1.5849625007211561814537389439478……可以取x≈1.585+2=3.585....