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JEE Advanced · Mathematics · 17. Properties of Triangles

In a non-right-angled triangle ΔPQR, let p,q,r denote the lengths of the sides opposite to the angles at P,Q,R respectively. The median from R meets the side PQ at S, the perpendicular from P meets the side QR at E, and RS and PE intersect at 0. If p=3,q=1, and the radius of the circumcircle of the ΔPQR equals 1, then which of the following options is/are correct?

  1. A Length of RS=72
  2. B Area of ΔSOE=312
  3. C Radius of incircle of ΔPRQ=322-3
  4. D Length of OE=16
Verified Solution

Answer & Solution

Correct Answer

(A) Length of RS=72

Step-by-step Solution

Detailed explanation



By sine rule in PQR

psinP=qsinQ=rsinR=2R

3sinP=1sinQ=1sinR=21

sinP=32 and sinQ=sinR=12

P=60° or 120°, Q=30° and 150°

As PQR is not a right angle triangle

Only possibility is P=120°, Q=R=30°

PQR is an isosceles triangle, hence, PE is also a median and O will be centroid.

( PQE and PRE are congruent and E is mid point of QR )

r=q=1, P=3

Option A:

Length of median from R

RS=122p2+2q2-r2=12232+2(1)-1=72

Option B:

Now, area of ΔSEF=14ΔPQR ...i

and area of ΔSOE=13ΔSEF ...ii

from i and ii ΔSOE=112ΔPQR ...iii

ΔPQR=12pq sinR=12×3×1×12=34

ΔSOE=112ΔPQR=348

Option D:

Length of OE

As O is centroid OE will be 13 of PE

PE=122q2+2r2-p2=122+2-3

=12

OE=13 PE=16

Option C:

Radius of incircle =ΔS i.e.areasemi-perimeter

=341+1+32

=322+3

=322-3
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