二分之根号下1加cos30°
=[√(1+cos30°)]／2
=√[2（cos15°）^2 ]/2
=( √2/2)cos 15°
= ( √2/2)cos(45°-30°)
=( √2/2)(cos45°*cos30°+sin45°*sin30°)
=( √2/2)（√6+√2）/4
=(√3+1)/4