Question

已知sin(π/6+a)=1/4求sin(π/6-2a) 急求答案

Answer 1

sin(π/6+α)=1/4

由二倍角公式可得,

cos(π/3+2α)=1-sin²(π/6+α)=15/16

∴sin(π/6-2α)=sin[π/2 - (π/3+2α)]

= cos(π/3+2α)

=15/16.