?x???23. （Ⅰ）??y????x???（Ⅱ）??y???23232?tcos? (t为参数）…………………………………… 4分
?tsin??tcos??tsin?3232 (t为参数）代入x2?y2?1，得
t?(3cos??3sin?)t?2?0 ，??0?sin(???6)?63
1PM?1PN?1t1?1t2?t1?t2t1t2?(3cos??3sin?)2?3sin(???6)??2,3
?…………10分
24.（Ⅰ）M??x|0?x?1?，a,b?M,
……………………………………… 4分
?0?a?1,0?b?1
ab?1?a?b?(a?1)(b?1)?0?ab?1?a?b（Ⅱ）h?2a,h?a?bab,h?2b2
h?34(a?b)ab?4(a?b)ab2?4?2abab?8
h??2,???………………………………………… 10分
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