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[1/1 Formula]
    Work: Calculate the value of equation 4*(cos(2*π/7))^2+4*(cos(4*π/7))^2+4*(cos(8*π/7))^2 .
    Question type: Mathematical calculation
    Solution:
          4*(cos(2*π/7))^2+4*(cos(4*π/7))^2+4*(cos(8*π/7))^2
        =4*(cos0.897598)^2+4*(cos(4*π/7))^2+4*(cos(8*π/7))^2
        =4*0.62349^2+4*(cos(4*π/7))^2+4*(cos(8*π/7))^2
        =4*0.62349^2+4*(cos1.795196)^2+4*(cos(8*π/7))^2
        =4*0.62349^2+4*(-0.222521)^2+4*(cos(8*π/7))^2
        =4*0.62349^2+4*(-0.222521)^2+4*(cos3.590392)^2
        =4*0.62349^2+4*(-0.222521)^2+4*(-0.900969)^2
        =4*0.3887397801+4*(-0.222521)^2+4*(-0.900969)^2
        =4*0.3887397801+4*0.049515595441+4*(-0.900969)^2
        =4*0.3887397801+4*0.049515595441+4*0.811745138961
        =1.554959+4*0.049515595441+4*0.811745138961
        =1.554959+0.198062+4*0.811745138961
        =1.554959+0.198062+3.246981
        =1.753021+3.246981
        =5.000002
    Answer:4*(cos(2*π/7))^2+4*(cos(4*π/7))^2+4*(cos(8*π/7))^2=5.000002
    Note: Radian

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