matlab plot语句在绘图时能不能标出特定（几个）点的值？

matlab plot语句在绘图时能不能标出特定（几个）点的值？比如y=sin(x),在x=pi/2和x=0.75pi这两个点标出y的值

x = linspace(0,2*pi,1000);
y = sin(x);
hold on;
plot(x,y,'k-');
posx = [pi/2 0.75*pi];
posy = sin(posx);
for i = 1:size(posx,2)
text(posx(i),posy(i),num2str(posy(i)));
end