求tan-15°等多少,cos45°*tan-15°等多少?知道的速度.重赏,.baidu{font-size:14px;line-height:1.5;}a{color:#0000cc;}a.t{color:#006633;font-size:14px;text-decoration:none;}a.cn{color:#555555;}

Answer 1

tan-15=-tan15=-(sin15)/cos15= =-[√(1-cos30)]/[√(1+cos30)] =-√[(1-cos30)^2/(1-cos30^2)] =-√[7-4√3] =-√[(2-√3)^2] =-2+√3cos45=(√2)/2即cos45*tan-15=(-2+√3)*((√2)/2) ...