是30º12'还是30.12º?cos30º12'=cos(π/6+π/900)≈cos(π/6)-sin(π/6)*(π/900)=√3/2-π/1800≈0.86428cos30.12º=cos(π/6+π/1500)≈cos(π/6)-sin(π/6)*(π/1500)=√3/2-π/3000≈0.86498...