cos（5π/8）*cos（π/8）=-sin（π/8）*cos（π/8）
又∵sin（π/4）=2sin（π/8）*cos（π/8）
∴cos（5π/8）*cos（π/8）=-sin（π/8）*cos（π/8）=-1/2（sin（π/4））
最后的答案应该是
负的四分之根号二
cos（5π/8）*cosπ/8
1个回答
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