If xi>0 for 1≤i≤n and x1+x2+....+xn=π then the greatest value of the sum sinx1+sinx2+...+sinxn is equal to
x1+x2+..xn=π
is greatest when
x1=x2=..xn=X.
Hence
π=nX
Or
x=πn
Hence greatest value of sin(x1)+sin(x2)+...sin(xn)
=nsin(X)
=nsin(πn).