Such as trapezoidal ABCD, AC is diagonal, and there are three corners with a vertex: ∠ DAC, ∠ Cab, ∠ DAB;

There is an angle with b as the vertex: ∠ b;

There are three angles with C as the vertex: ∠ BCA, ∠ ACD, ∠ BCD;

The vertex of an angle is d: ∠ d.

A * * * has 3+ 1+3+ 1=8.