Solution: 1 For example, a quadrilateral ABCD, ∠A= 120 degrees, ∠B=80 degrees, ∠C=60 degrees, ∠D= 100 degrees.

Diagonal angles ∠A+∠C= 180 degrees, ∠B+∠D= 180 degrees, ∠A and ∠C, ∠B and ∠D are complementary angles respectively, but

2.2 > 1, when both sides are multiplied by-1, the left 2 *( 1)=-2, and the right 1 *( 1)=- 1, -2.