Read the following two statements which are taken as axioms: (i) If two lines intersect each other, then the vertically opposite angles are not equal. (ii) If a ray stands on a line, then the sum of two adjacent angles so formed is equal to 180°. Is this system of axioms consistent? Justify your answer.

Question

Philoid · Accepted Answer

We know that, if two lines intersect each other, then the vertically opposite angles are equal. It is a theorem. So, given statement I is false and not an axiom.

Also, we know that, if a ray stands on a line, then the sum of two adjacent angles so formed is equal to 180°. It is an axiom. So, given statement II is true and an axiom.

Thus, in given statement, first is false and second is an axiom. Hence, given system of axioms is not consistent.