Question

Which of the following is an invalid quadrilateral?

(a) ▀ABCD ∠A=60,∠B=120,∠C=120,∠D=90

(b) ▀PQRS ∠A=90,∠B=90,∠C=90,∠D=90

(c) ▀LMNO ∠A=90,∠B=150,∠C=60,∠D=60

(d) ▀EFGH ∠A=100,∠B=20,∠C=120,∠D=120

This question was addressed to me in an online quiz.

The query is from Geometry topic in section Practical Geometry of Mathematics – Class 8

Answer 1

The correct choice is (a) ▀ABCD ∠A=60,∠B=120,∠C=120,∠D=90

Best explanation: The basic property of any quadrilateral is that the sum of all the internal angles is 360°. Here except ▀ABCD the sum of all the internal angles of other quadrilaterals is equal to 360°. Hence all the other quadrilaterals except ▀ABCD are incorrect.