y=sinx
y'=cosx
点p(π/3,1/2)的切线斜率是k=cos(π/3)=1/2
所以过这点的切线垂直的直线的斜率是k=-1/(1/2)=-2
所以y-1/2=-2(x-π/3)
即y=-2x+2π/3+1/2