题目内容
已知
A.

B.

C.

D.

【答案】分析:由已知中
且α是第三象限的角,我们易根据诱导公式求出sinα,cosα,再利用诱导公式即可求出cos(2π-α)的值.
解答:解:∵
且α是第三象限的角,
∴
,
∴
∴cos(2π-α)=
故选B
点评:本题考查的知识点是运用诱导公式化简求值,熟练掌握诱导公式是解答本题的关键,解答中易忽略α是第三象限的角,而选解为D

解答:解:∵

∴

∴

∴cos(2π-α)=

故选B
点评:本题考查的知识点是运用诱导公式化简求值,熟练掌握诱导公式是解答本题的关键,解答中易忽略α是第三象限的角,而选解为D

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