Tính giá trị của G = cos^2 pi/6 + cos^2 2pi/6 +...+ cos^2 5pi/6 + cos^2 pi

Đáp án A

G=cos2π6+cos22π6+...+cos25π6+cos2π=cos2π6+cos22π6+cos24π6+cos25π6+cos2π2+cos2π=cos2π6+cos2π3+cos22π6+cos2π6+1=2cos2π6+cos22π6+1=2cos2π6+cos2π6+1=3