Four points, A, B, C, D, yield six lines: AB, AC, AD, BC, BD, CD. These lines form twelve angles: ∠ABC, ∠ABD, ∠ACD, ∠BCD, ∠CAB, ∠DAB, ∠BCA, ∠CBA, ∠DAC, ∠CDB, ∠ADB, and ∠BDA. Class 6 NCERT Ganita Prakash Chapter 2 Lines ...