Question

各位大神求解第13题。

各位大神求解第13题。这里高中数学初学者...所以尽量有过程昂，谢谢😉

Answer 1

13.
cos(5π/6 +α)-sin²(α-π/6)
=-cos[π-(5π/6 +α)]-[1-cos²(α-π/6)]
=-cos(π/6 -α)-1+cos²(α-π/6)
=cos²(π/6-α)-cos(π/6 -α)-1
=(√3/3)²-(√3/3)-1
=-(2+√3)/3