- A54
- B60
- C66
- D120
Step-by-Step Solution
∠A and ∠B are consecutive (adjacent) angles, so they are supplementary. ∠B = 180 − 120 = 60°.
Answer: B) 60
In parallelogram ABCD, ∠A = 120°. Find ∠B in degrees.
Class 8Understanding QuadrilateralsQuadrilaterals
Key idea: Special parallelograms — extra properties
**Rectangle**: parallelogram + all angles 90°. Extra: diagonals are equal in length.
**Rhombus**: parallelogram + all sides equal. Extra: diagonals are perpendicular AND bisect the angles at each vertex.
**Square**: parallelogram + all angles 90° + all sides equal. Has both extras: equal AND perpendicular AND angle-bisecting diagonals.
Knowing the family tree saves you memorising overlapping rules — a square inherits everything from rectangle AND rhombus.
**Rhombus**: parallelogram + all sides equal. Extra: diagonals are perpendicular AND bisect the angles at each vertex.
**Square**: parallelogram + all angles 90° + all sides equal. Has both extras: equal AND perpendicular AND angle-bisecting diagonals.
Knowing the family tree saves you memorising overlapping rules — a square inherits everything from rectangle AND rhombus.
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 Understanding Quadrilaterals practice questions
More Class 8 Understanding Quadrilaterals practice
Which property is NOT necessarily true for every parallelogram?In parallelogram ABCD, side AB = 8 cm. What is the length of side CD?The diagonals of a parallelogram bisect each other. If one diagonal is 14 cm, each half…Assertion (A): A square is a rectangle. Reason (R): A rectangle is a parallelogram with…Two adjacent angles of a parallelogram are equal. What is the measure of each, in degrees?