(1)∵DA=DA'∴△DAA'是等腰三角形∴∠A=∠A'∵∠1=∠A+∠A'∴∠1=2∠A'
(2)∵EA=EA'DA=DA连接AA'∴△DAA',△EAA'是等腰三角形∵∠1=∠DA'A+∠DA'A,∠2=∠EAA'+∠EA'A∴∠1+∠2=2∠A'
(3)连接AA'∵DA=DA'∴△DAA'是等腰三角形∴∠DAA'=∠DA'A∵EA=EA'∴△EAA'是等腰三角形∴∠EAA'=∠EA'A∴∠2=∠EAA'+∠EA'A∵∠1=2∠DAA'∵2∠DA'A=2∠A'+2∠EAA'∴∠1=2∠A'+∠2∴∠1-∠2=2∠A