(不用圆的知识做，单纯导角)
已知一个四边形ABCDABCDABCD 1.若对角互补，求证∠ABC=∠ABD\angle ABC=\angle ABD∠ABC=∠ABD 2.若∠ABC=∠ABD\angle ABC=\angle ABD∠ABC=∠ABD,求证∠BAC=∠BDC\angle BAC=\angle BDC∠BAC=∠BDC
