One-year practice test for the whole school, seventh grade, volume 2, mathematics, 5 1 page, the third question in the classroom test.
It is feasible, because ∠BAM=∠CAB, ∠ABN=∠ABC, △ABC and △ABD have the same edge, so △ ABC △ Abd, because △ ABC △ Abd, so AC = AD. Another method, let the height of AB side in △ABC intersect at X point, extend line CX, make straight line GH perpendicular to line CX, make ∠HGJ=∠CAB, make ∠GHK=∠CBA, line GL = AC, HL = BC.