已知双曲线
=1(a>0,b>0)的动弦BC平行于虚轴,M、N是双曲线的左、右顶点,
0 53349 53357 53363 53367 53373 53375 53379 53385 53387 53393 53399 53403 53405 53409 53415 53417 53423 53427 53429 53433 53435 53439 53441 53443 53444 53445 53447 53448 53449 53451 53453 53457 53459 53463 53465 53469 53475 53477 53483 53487 53489 53493 53499 53505 53507 53513 53517 53519 53525 53529 53535 53543 266669
(1)求直线MB、CN的交点P的轨迹方程;
(2)若P(x1,y1),B(x2,y2),求证:a是x1、x2的比例中项.