摘要：28． 解:(1)抛物线与y轴的交于点B. 令x=0得y=2． ∴B(0.2) ············································· 1分 ∵ ∴A··········································· 3分 (2)当点P是 AB的延长线与x轴交点时. ．············································· 5分 当点P在x轴上又异于AB的延长线与x轴的交点时. 在点P.A.B构成的三角形中.． 综合上述: ················································································ 7分 (3)作直线AB交x轴于点P.由(2)可知:当PA-PB最大时.点P是所求的点 ····· 8分 作AH⊥OP于H． ∵BO⊥OP. ∴△BOP∽△AHP ∴ ····································································································· 9分 由(1)可知:AH=3.OH=2.OB=2. ∴OP=4.故P(4.0) ···················································································· 10分 注:求出AB所在直线解析式后再求其与x轴交点P(4.0)等各种方法只要正确也相应给分．

网址：http://m.1010jiajiao.com/timu_id_2042863[举报]