With reference to the figure below, consider the two statements:
Statement 1: The points A, B, and C will lie on a straight line if x + y = 180∘.
Statement 2: The angle on a straight line is 180∘.
Both the statements are true and statement 2 is the correct explanation of statement 1.
The angle on a straight line is 180∘. Adjacent angles on a straight line add up to 180∘.
Conversely, if adjacent angles add up to 180∘ then the angles are on a straight line.
Hence, if x + y = 180∘ , then A, B and C lie on a straight line.
Therefore, both the statements are true and statement 2 is the correct explanation of statement 1.