向量运用三角函数
证明恒等式: (1)(1-sin2x)/(cos^2x-sin^2x)=(1-tanx)/(1+tanx) (2)(tanx+tany)/(tanx-tany)=sin(x+y)/sin(x-y)
(1)(1-sin2x)/(cos^2x-sin^2x)=(1-2sinxcosx)/(cos^2x-sin^2x) =[(cosx-sinx)^2]/[(cosx-sinx)(cosx+sinx)] =(cosx-sinx)/(cosx+sinx) =(1-tanx)/(1+tanx) (分子、分母同除以cosx) (2)(tanx+tany)/(tanx-tany) [分子、分母同乘以cosxcosy] =(sinxcosy+cosxsiny)/(sinxcosy-cosxsiny) =sin(x+y)/sin(x-y)
问:小华5/1小时行了3/2千米他行1千米需要多少小时,他行1小时可行多少千米?(为...
答:1/5÷2/3=1/5×3/2=3/10小时详情>>
问:甲车每小时行38km乙车每小时行41km甲乙车同时两地开岀相向行了2.5小时后相...
答:(38+41)x2.5=197.5千米详情>>