1)这条直线通过顶点A,那么设这条直线为AD交BC于D
设∠B=∠BAD=∠C=x
∠CAD=∠CDA=∠B+∠BAD=2x
∠CAD+∠CDA+∠C=5x=180
x=36度,
∠BAC=3x=108°,∠B=∠C=36°
2)这条直线通过顶点B(或C),那么不妨设直线为BE交AC于E
∠A=∠ABE=y
∠ABC=∠BEC=∠C=∠A+∠ABE=2y
∠A+∠ABC+∠C=5y=180°
y=36°
∠A=36°