cos(9π/4)+tan(-7π/6)+sin(21π)=
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cos(9π/4)+tan(-7π/6)+sin(21π)=
![cos(9π/4)+tan(-7π/6)+sin(21π)=](/uploads/image/z/11538774-54-4.jpg?t=cos%EF%BC%889%CF%80%2F4%29%2Btan%EF%BC%88-7%CF%80%2F6%EF%BC%89%2Bsin%EF%BC%8821%CF%80%EF%BC%89%3D)
cos(9π/4)+tan(-7π/6)+sin(21π)
=cosπ/4-tan(π/6)+0
=√2/2-√3/3
再问: sin21π怎么化?
再答: sin(21π)=sin(20π+π)=sinπ=0
=cosπ/4-tan(π/6)+0
=√2/2-√3/3
再问: sin21π怎么化?
再答: sin(21π)=sin(20π+π)=sinπ=0
cos(9π/4)+tan(-7π/6)+sin(21π)=
sin(-21π/4) cos(-20π/3) tan(-19π/6)=
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