If P(x, y) is any point of hyperbola, then y? =b? ( 1 -x? /a? ); Kpm=(y-y0)/(x-x0),Kpn =(y+y0)/(x+x0);
kpm * Kpn =[(y-y0)/(x-x0)]*[(y+y0)/(x+x0)]=(y? -What about you? )/(x? -x0)=b? (x0? /a? -x? /a? )/(x? -x0? )=-b? /a? ;