cosπ/11×cos2π/11×cos3π/11×cos4π/11×cos5π/11=?求值cosπ/11×cos2π/11×cos3π/11×cos4π/11×cos5π/11=?求值 最后几步由sin6π/11×cos5π/11到sin10π/11怎样变得

求COSπ/5*COS2π/5 cosπ/5×cos2π/5= COSπ/5乘以COS2π/5 cosπ/5×cos2π/5 cosπ/5cos2π/5 cosπ/5cos2π/5=? cosπ/5 - cos2π/5 怎样变成 cosπ/5 + cos2π/5rt 化简cos2α+cos2(π/3+α)+cos2(π/3-α)化简cos²α+cos²（π/3+α）+cos²（π/3-α） cosπ/11*cos2π/11*cos3π/11*cos4π/11*cos5π/11上式为何等于cosπ/11*cos2π/11*cos4π/11*cos8π/11*cos16π/11 sinπ.cosπ.sin2π.cos2π分别是多少 cosπ/9*cos2π/9*cos4π/9=? 求值:cosπ/7*cos2π/7*cos3π/7 cosπ/7cos2π/7cos3π/7=? cosπ/7cos2/7πcos4/7π= cosπ/9cos2π/9cos23π/9 （cosπ/5）（cos2π/5)的值等于 cosπ/5·cos2π/5等于多少? cosπ/5*cos2π/5的值等于