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Analysis of exercises in junior high school mathematics monthly exam
Solution: the bisector of ∵∠ABC and ∠ACB intersects at point E,

∴∠MBE=∠EBC,∠ECN=∠ECB,

∫MN∨BC,

∴∠EBC=∠MEB,∠NEC=∠ECB,

∴∠MBE=∠MEB,∠NEC=∠ECN,

∴BM=ME,EN=CN,

∴MN=ME+EN,

That is Mn = BM+cn.

∫BM+CN = 9

∴MN=9,