化解之后得=2根号2-4cosa-1+tana+3
=2根号2+2-4cosa+tana
a是锐角,且sin（A+15度）=2分之根号3,得a=45°
把a=45°代入2根号2+2-4cosa+tana
=2根号2+2-4x根号2分之2+1
=2根号2+2-2根号2+1
=3