······9分除此之外,当30CPQ B? ????时,QPC ABC△∽△,此时3tan303CQCP? ??.101cos602AMAP? ???,2 2AP AM t? ??.2 2CP t? ??.·························10分3cos302BNBQ? ???,2 3(3 )332BNBQ t? ???.又2 3BC??,2 3 2 32 3 (3 )3 3tCQ t? ????.···································11分2 3332 2 3tt? ??,12t?.?当12t?s或34s时,以C P Q,,为顶点的三角形与ABC△相似.················12分7、(08四川巴中30题)(12分)30.已知:如图14,抛物线2334y x?? ?与x轴交于点A,点B,与直线34y x b?? ?相交于点B,点C,直线34y x b?? ?与y轴交于点E.(1)写出直线BC的解析式.(2)求ABC△的面积.(3)若点M在线段AB上以每秒1个单位长度的速度从A向B运动(不与A B,重合),同时,点N在射线BC上以每秒2个单位长度的速度从B向C运动.设运动时间为t秒,请写出MNB△的面积S与t的函数关系式,并求出点M运动多少时间时,MNB△的面积最大,最大面积是多少?解:(1)在2334y x?? ?中,令0y?233 04x?? ??12x? ?,22x??( 2 0)A? ?,,(2 0)B,·········································1分又?点B在34y x b?? ?上xyABCEMDPNO
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