Two adjacent angles share a common vertex and a common side. Which additional condition makes them a linear pair?

Class 7Lines and AnglesLines and Angles

ATheir non-common sides form a straight line.
BTheir measures are equal.
CBoth are right angles.
DThey are vertically opposite.

Step-by-Step Solution

A linear pair is two adjacent angles whose non-common (outer) sides together form a straight line; they are supplementary.

Answer: A) Their non-common sides form a straight line.

Key idea: Vertically opposite angles

When two straight lines cross, four angles form at the intersection. The two angles directly **across** the vertex (sharing only the vertex, not a side) are called **vertically opposite** — and they are always equal.

If one angle is 70°, then:
- Its vertical opposite is also 70°.
- The other two angles are each 110° (linear pair with 70°).

Why? Each pair forms a linear pair with a common neighbour, both summing to 180° — so the opposites end up equal.

Master this chapter in 30 minutes a day.

Don't just memorise the answer — build a daily practice habit.

Practice 5 Similar Questions Free →

All Lines and Angles practice questions

More Class 7 Lines and Angles practice

Assertion (A): When a transversal cuts two parallel lines, each pair of co-interior…Assertion (A): Vertically opposite angles are always equal. Reason (R): Each of them…Two lines intersect such that one of the four angles formed is a right angle. What can…Two parallel lines are cut by a transversal. A pair of co-interior angles measures (2x)°…Which statement about adjacent angles is correct?