- A90
- B99
- C180
- D81
Step-by-Step Solution
Remaining sum = 360 − (100 + 80) = 180°. The two equal angles share this: 180 / 2 = 90° each.
Answer: A) 90
Two angles of a quadrilateral are 100° and 80°, and the remaining two angles are equal. Find each of the equal angles 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.
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