计算cosπ/5*cos3π/10-sinπ/5*sin3π/10
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计算cosπ/5*cos3π/10-sinπ/5*sin3π/10
计算cosπ/5*cos3π/10-sinπ/5*sin3π/10
计算cosπ/5*cos3π/10-sinπ/5*sin3π/10
cos(A-B)=cosAcosB+sinAsinB
A=π/5
B=3π/10
计算cosπ/5*cos3π/10-sinπ/5*sin3π/10
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