三角函数
解：原式=[(sin15-cos15)/cos15]/[(sin15+cos15)/cos15] ````````=(sin15-cos15)(sin15+cos15)/(sin15+cos15)² ````````=(sin²15-cos²15)/(1+2sin15cos15) ````````=-cos30/(1+sin30) ````````=-(√3/2)/(1+1/2) ````````=-√3/3