Answer Verified Consider trapezium ABCD such that AB is parallel to CD and $AD = BC$.Consider two points M and N that can be considered as the foot of perpendicular drawn on AB from vertices D and C respectively.Now, if we compare $\Delta DAM$and $\Delta CBN$, we have:$AD = BC{\text{ }}...{\text{(Given)}}$$\angle AMD = \angle BNC{\text{ }}...{\text{(Right angles i}}{\text{.e}}{\text{. 9}}{{\text{0}}^ \circ }{\text{)}}$And $DM = CN{\text{ }}....{\text{(Distance between two parallel lines)}}$From this we can say that both the triangles are congruent.$\Delta DAM \cong \Delta CBN$We know that corresponding parts of congruent triangles are equal. So we have: $ \Rightarrow \angle A = \angle B .....(i)$Also $\angle B + \angle C = {180^ \circ }{\text{ }}...{\text{(sum of co - interior angles)}}$Substituting the value of $\angle B$ from equation first, we have:$ \Rightarrow \angle A + \angle C = {180^ \circ } ....(ii)$Equation $(ii)$ shows that the sum of the pair of opposite angles of trapezium ABCD is ${180^ \circ }$.Therefore the trapezium is a cyclic quadrilateral.Note: A quadrilateral is said to be cyclic quadrilateral if all of its 4 vertices lie on the same circle.Read More Vedantu Improvement Promise When the non-parallel sides of a trapezium are equal then it is known as
When the non-parallel sides of a trapezium are equal then it is known as an isosceles trapezium Concept: Area of Trapezium Is there an error in this question or solution?
Solution: We know that, if the sum of a pair of opposite angles of a quadrilateral is 180°, the quadrilateral is cyclic. Draw a trapezium ABCD with AB || CD AD and BC are the non-parallel sides that are equal. AD = BC. Draw AM ⊥ CD and BN ⊥ CD. Consider ΔAMD and ΔBNC AD = BC (Given) ∠AMD = ∠BNC (90°) AM = BN (Perpendicular distance between two parallel lines is same) By RHS congruence, ΔAMD ≅ ΔBNC. Using CPCT, ∠ADC = ∠BCD.....(1) ∠BAD and ∠ADC are on the same side of transversal AD. ∠BAD + ∠ADC = 180° ∠BAD + ∠BCD = 180° [From equation(1)] This equation proves that the sum of opposite angles is supplementary. Hence, ABCD is a cyclic quadrilateral. ☛ Check: NCERT Solutions Class 9 Maths Chapter 10 Video Solution: Maths NCERT Solutions Class 9 Chapter 10 Exercise 10.5 Question 8 Summary: If the non-parallel sides of a trapezium are equal, then it is a cyclic quadrilateral ☛ Related Questions: Math worksheets and
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