∴∠4=∠3=∠1+∠2=2∠2.
由三角形的内角和定理,得∠2+∠4+∠BAC=180º,解得∠4=78º,
则∠DAC=180º-2∠4=24º.
As teenagers, we're old enough ________ with housework. We can help set the table, wash the dishes and clean our own rooms.
下列关于化学发展的看法错误的是( )