三角函数正弦值,余弦值比较大小 cos15π/8与cos14/9πcos515`与cos530`sin(-54π/7)与sin(-63π/8)

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三角函数正弦值,余弦值比较大小 cos15π/8与cos14/9πcos515`与cos530`sin(-54π/7)与sin(-63π/8)

三角函数正弦值,余弦值比较大小 cos15π/8与cos14/9πcos515`与cos530`sin(-54π/7)与sin(-63π/8)
三角函数正弦值,余弦值比较大小
cos15π/8与cos14/9π
cos515`与cos530`
sin(-54π/7)与sin(-63π/8)

三角函数正弦值,余弦值比较大小 cos15π/8与cos14/9πcos515`与cos530`sin(-54π/7)与sin(-63π/8)
cos15π/8=cos(2π-15π/8)=cos(π/8)
cos14/9π=cos(2π-14π/9)=cos(4π/9)
cosx在[0,π]是减函数,所以cos(π/8)>cos(4π/9)
即cos15π/8>cos14/9π
cos515°=cos155°
cos530°=cos170°
同理cos155°>cos170°
sin(-54π/7)=sin(2π/7)
sin(-63π/8)=sin(π/8)
sinx在[0,π/2]为增函数
所以sin(2π/7)>sin(π/8)
即sin(-54π/7)>sin(-63π/8)