21. In triangle ABC, midpoints of sides AB AC and BC are
P.Q and R respectively. AS LBC
Prove that OPQRS is a cyclic quadrilateral
SR
Fig. 2.102
195
Answers
Answer:
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Step-by-step explanation:
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Given:In △ABCP,Q and R are the midpoints of the sides
BC,CA and AB respectively.
Also,AD⊥BC
In a right-angled triangle, ADP,R is the midpoint of AB
∴RB=RD
⇒∠2=∠1 ........(1)
since angles opposite to the equal sides are equal.
Since,R and Q are the mid-points of AB and AC, then RQ∥BC
or RQ∥BP (by mid-point theorem)
Since,QP∥RB then quadrilateral BPQR is a parallelogram,
⇒∠1=∠3 ........(2)
since angles opposite to the equal sides are equal.
From equations (1) and (2),
∠2=∠3
But ∠2+∠4=180
∘
(by linear pair axiom)
∠3+∠4=180
∘
(∵∠2=∠3)
Hence ,quadrilateral PQRD is a cyclic quadrilateral.
So,points P,Q,R and D are con-cyclic.
Hence the statement is true.
The answer is 0