Let \(L=0\) be the chord of contact of \((5,1)\) with respect to the circle
\[
S\equiv x^2+y^2+8x+10y-8=0.
\]
If the pole of \(L=0\) with respect to the circle
\[
S'\equiv x^2+y^2+4y-21=0
\]
is \((-k,-h)\), then \(k+h=\)
Show Hint
For the circle
\[
x^2+y^2+2gx+2fy+c=0,
\]
the polar of \((x_1,y_1)\) is
\[
\boxed{
xx_1+yy_1+g(x+x_1)+f(y+y_1)+c=0.
}
\]
Compare the coefficients of the given line with the polar equation to determine the pole.