Question: what is the condition to make a triangle

title: Triangle
text: P A  ̄ ⋅ Q A  ̄ C A  ̄ ⋅ A B  ̄ + P B  ̄ ⋅ Q B  ̄ A B  ̄ ⋅ B C  ̄ + P C  ̄ ⋅ Q C  ̄ B C  ̄ ⋅ C A  ̄ = 1 . ( \ displaystyle ( \ frac ( ( \ overline ( PA ) ) \ cdot ( \ overline ( QA ) ) ) ( ( \ overline ( CA ) ) \ cdot ( \ overline ( AB ) ) ) ) + ( \ frac ( ( \ overline ( PB ) ) \ cdot ( \ overline ( QB ) ) ) ( ( \ overline ( AB ) ) \ cdot ( \ overline ( BC ) ) ) ) + ( \ frac ( ( \ overline ( PC ) ) \ cdot ( \ overline ( QC ) ) ) ( ( \ overline ( BC ) ) \ cdot ( \ overline ( CA ) ) ) ) = 1 . )