Question

cosπ/12，cos（-31π/12）函数值是多少？哪位帮忙解决

Answer 1

2（cosπ/12）^2 -1=cosπ/6=(3^(1/2))/2
解方程即可
cos（-31π/12）=cos(7π/12)=cos(π/2)（cosπ/12）-(sinπ/2)sinπ/12=-sinπ/12
由上题可得

Answer 2

cos(π/6)=2cos^2(π/12)-1
cos(π/12)=√(√3+2)/2

cos（-31π/12）
=cos（7π/12）
=-sin（π/12）
=√(2-√3)/2

Answer 3

用cos（π/3-π/4）cos（-31π/12）=cos（2π+7π/12）=cos（π/3+π/4）

Answer 4

cos pi/12 = cos (pi/6 / 2) = sqrt((1+cos6pi)/2) = sqrt((1+sqrt(3)/2))/2) = sqrt((2+sqrt(3))/2
cos(-31pi/12) = cos(31pi/12) = cos(2pi+7pi/12) = cos (pi/2 + pi/12) = sin(pi/12)
=sqrt((2-sqrt(3))/2)

Answer 5

√(2-√3)/2