Question

設(shè)k∈Z,下列等式中正確的個(gè)數(shù)是（　�。�

①sin(kπ+α)=(-1)^k·sinα；②cos(kπ+α)=(-1)^k·cosα；③tan(kπ+α)=(-1)^k·tanα；④cot(kπ+α)=(-1)^k·cotα

A．1         B．2      C．      3D．4

      

Answer 1

答案：B

       解析：通過(guò)對(duì)n分奇偶進(jìn)行討論可知①②正確.