已知π/6已知π/6
已知π/6sin(2π/3—a)=sin[π-(2π/3—a)]=sin(π/3+a)π/6
n(2π/3—a)=sin[π-(2π/3—a)]=sin(π/3+a)π/6sin²(π/3+a)+cos²(a+π/3)=1所以sin(π/3+a)=√(1-m²)所以sin(2π/3 -a)=√(1-m²)