如图,$\angle 1 = \angle 2 = \angle 3 = 5 0 ^ {\circ} $,则∠4的度数是.
利用平行线的性质和判定时,一定要清楚由角的关系推出平行关系是平行线的判定,由平行关系得到角的关系是平行线的性质.
如图,∵$\angle 1 = \angle 2 = 5 0 ^ {\circ} $,∴$\angle N F E = \angle 1 = $ $5 0 ^ {\circ} = \angle 2 $,∴$A B / / C D $,∴$\angle 4 = \angle N E C $.∵$\angle N E C = 1 8 0 ^ {\circ} - $ $\angle 3 = 1 8 0 ^ {\circ} - 5 0 ^ {\circ} = 1 3 0 ^ {\circ} $,∴$\angle 4 = 1 3 0 ^ {\circ} $. 故答案为130°.