sin(pi/7)^2+sin(2pi/7)^2+sin(3pi/7)^2=怎么算

三角函数恒等变形证明sin( pi/3 ) + sin( 2*pi/3) + ...+ sin( n * pi/3)= 化简：sin(2pi-a)sin(pi+a)cos(-pi-a)/sin(3pi-a)cos(pi-a) Matlab u(x,t)=sin(5*pi*x)cos(5*pi*t)+2sin(7*pi*x)cos(7*pi*t) tana=2求sin(pi-a)cos(2pi-a)sin(-a+3pi/2)/tan(-a-pi)sin(-pi-a) log((sin(5))^2)-3+pi=? log((sin(30))^2)-3+pi= 证明sin(pi/n)*sin(2pi/n)*sin(3pi/n)*…sin((n-1)pi/n)=n/(2^(n-1) 已知函数f（x）=cos（2x-pi/3）+2sin（x-pi)*sin(x+pi/4) 化简间sin（a-2pi)cos(a+pi）tan(a-99pi)cos(pi-a)sin(3pi-a)sin（-a-p 已知Sin(2x+pi/3)=1/3,求Sin(5Pi/6-4x), y=sin(x+pi/3)sin(x+pi/2)的最小正周期是什么 sin（pi/2+x）=?