如图,已知a//b,∠1=50°,则∠2=( )
A:40°
B:50°
C:120°
D:130°
9()()8109 ____
(Ⅰ)求不等式﹣2<f(x)<0的解集A;
(Ⅱ)若m,n∈A,证明:|1﹣4mn|>2|m﹣n|.