(1)3以下(2)1以下という感じはします。 (1) cos(2π/9)+cos(4π/9)+cos(8π/9) https://www.wolframalpha.com/input?i=cos%282%CF%80%2F9%29%2Bcos%284%CF%80%2F9%29%2Bcos%288%CF%80%2F9%29&lang=ja (2) cos(2π/9)*cos(4π/9)*cos(8π/9) https://www.wolframalpha.com/input?i=cos%282%CF%80%2F9%29*cos%284%CF%80%2F9%29*cos%288%CF%80%2F9%29&lang=ja
(1)3以下(2)1以下という感じはします。
(1)
cos(2π/9)+cos(4π/9)+cos(8π/9)
https://www.wolframalpha.com/input?i=cos%282%CF%80%2F9%29%2Bcos%284%CF%80%2F9%29%2Bcos%288%CF%80%2F9%29&lang=ja
(2)
cos(2π/9)*cos(4π/9)*cos(8π/9)
https://www.wolframalpha.com/input?i=cos%282%CF%80%2F9%29*cos%284%CF%80%2F9%29*cos%288%CF%80%2F9%29&lang=ja