婵炲本鍔栫粊锟�
20．(本题满分10分)
25?（x+3）?先化简，再求值：?x?2?，其中x?3． ??x?2?x?2?19．解：原式=5+5?2?1?2． ································································ （8分） =25?1．
x2?4?5x?220．解：原式=， ····························································· （5分） ?2x?2?x?3? =
?x?3??x?3??x?2x?2?x?3?2， ······················································· （1分）
=
x?3. ·················································································· （1分） x?33?3=3?2. 3?3当x?3时，原式=松江区
19．（本题满分10分） 计算：3?1?3?19．（本题满分10分） 计算：3?1?3?001?8．
3?21?8．
3?2解：原式=1?(3?1)?3?2?22……………………………（每个2分） =2?2……………………………………………………………2分
徐汇区
19. 计算：12?()?1?121?(??3.14)0?|23?4|. 3?1
杨浦区
19、（本题满分10分）
先化简，再求值：