Let P,Q,R,S as a mid point of side AB,BC,CD,DA of quadrilateral ABCD. Show that ABCD is a parallelogram.
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★ Let P,Q,R,S as a mid point of side AB,BC,CD,DA of quadrilateral ABCD. Show that ABCD is a parallelogram.
ar(||gm PQRS) = ½ar(quad.ABCD)
Join AC to AR
In ∆ABC, P and Q are the midpoints of the sides AB and AC respectively.
∴ PQ||AC and PQ=½AC
In ∆DAC, S and R are the midpoints of the sides AD and DC respectively.
∴ SR||AC and SR = ½AC
Thus, PQ || SR and PQ = SR
∴ PQRS is a Parallelogram
Now, medians AR devides ∆ACD into two ∆ of equal area
∴ ar(∆ARD) = ½ar(∆ACD)
Medians RS devides ∆ARD into two ∆ of equal area
∴ ar(∆DSR) = ½ar(∆ARD)
From (i) and (ii), we get ar(∆DSR) = ¼ar(∆ABC)
Similarly, ar(∆BPQ) = ¼ar(∆ABC)
∴ ar(∆DSR) + ar(∆BPQ) = ¼[ar(∆ACD)+ar(∆ABC)]
==> ar(∆DSR)+ar(∆BPQ) = ¼ar(quad. ABCD)
Similarly, ar(∆CRQ) + ar;∆ASp) = ¼ar(quad. ABCD)
Adding (iii) and (iv), we get
ar(∆DSR)+ar(∆BPQ)+ar(∆CRQ)+ar(∆ASP)+ar(||gm PQRS) = ar(quad. ABCD)
Substracting from (v) and (vi), we get
ar(||gm PQRS) = ½ar(quad. ABCD)
Hence, proved.
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