188.The diagonals of a quadrilateral ABCD intersect each other at point O such that Show that ABCD is a trapezium.
Given a quadrilateral ABCD in which AC and BD are diagonals, which intersect each other at O. To Prove : ABCD is a trapezium such that AB || DC.
Const : Draw a line OM || AB. Proof: In ∆ADB, we have OM || AB. Therefore, by using Basic proportionality theorem, we have
[Taking reciprocals of both sides] It is given that,
...(ii) Comparing (i) and (ii), we get
Therefore, by using converse of basic proportionality theorem, we have OM || DC But OM || AB (by construction) ⇒ AB || DC Hence, ABCD is a trapezium.
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189.State which pairs of triangles in the given Fig, are similar. Write the similarity criterion used by you for answering the question and also write the pairs of similar triangles in the symbolic form:
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Short Answer Type
190.
In the given fig. ∆ODC ~ ∆OBA, ∠BOC = 125° and ∠CDO = 70°. Find ∠DOC, ∠DCO and ∠OAB.