Given: ABCD is trapezium in which AD = BC
To prove: Opposite angles of ABCD are supplementary.
Construction: Draw BE || AD
Proof: ∵ Quadrilateral ABED is a parallelogram
AB || DC (Given) AD || BE (By construction).
| A quadrilateral is a parallelogram if its any pair of opposite sides are parallel and equal.
∴ ∠BAD = ∠BED
| Opposite angles of a parallelogram are equal
and AD = BE
| Opposite sides of a parallelogram are equal
But AD = BC | Given
∴ BE = BC
∴ ∠BEC = ∠BCE
| Angles opposite to equal sides of a triangle are equal
∴ ∠BEC + ∠BED = 180° | Linear pair
⇒ ∠BCE + ∠BED = 180°
⇒ ∠BAD + ∠BED = 180°
⇒ ∠ADE + ∠ABE = 180°
⇒ Opposite angles of ABCD are supplementary.
5. In the given figure, find the values of a, b, c and d. Given that ∠BCD = 43° and ∠BAE = 62°.