f(α)=[sin(π-α)cos(α-π)tan(-α+π)]/[tan(π+α)cos(3/2π+α)] 化简

问题描述:

f(α)=[sin(π-α)cos(α-π)tan(-α+π)]/[tan(π+α)cos(3/2π+α)] 化简

f(α)=[sin(π-α)cos(α-π)tan(-α+π)]/[tan(π+α)cos(3/2π+α)]
=sinα(-cosα)(-tanα)/(tanαsinα)
=cosαcos(3/2π+α)=sinα为什么?我怎么觉得是-sinαcos(3/2π+α)=sinα为什么?我怎么觉得是-sinα第四象限cos>0