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

问题描述:

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

f(α)=[sin(π-α)cos(2π-α)tan(-α+π)]/[-tan(-α-π)sin(-π-α)]
=[sinαcosα(-tanα)]/{tanα[-sin(π+α)}
=-sinαcosαtanα/(tanαsinα)
=-cosα不是cosα吗?不是