设P(x1,y1)延长PM交x于Q,延长PN交x于R因OA为y=kx(k>0,x>0),射线OB为y=-kx(x>0)PM⊥OA于M,PN⊥OB于N所以OR=2x1/k四边形ONPM=三角形PQR-三角形OMQ-三角形ONR k =x1^2/k-k((x1/k+y1)/(根号下k^2+1))^2/2-k((x1/k-y1)/(根号下k^2+1))^2/2 y=根号下x^2-k^2-1(x>=根号下k^2+1)