Question
Fri March 01, 2013 By:

ABCD is a square & angle PQR=90

Expert Reply
Wed March 06, 2013
Answer : Given : ABCD is a square & angle PQR=90 . 
P,Q,R are 3 points on AB,BC & CD respectively.AP=CR.
To Prove :
1.PB = QC
2.PQ=QR
3.Angle QPR=45
 
Let as assume that angle QPR =a and angle QRP = b
 
Now , in triangle PQR and triangle QCR
angle PQR = angle QCR = 90
angle PRQ = angle RQC = b .....(1) { opposite angles}
angle QPR = angle QRC = a....(2) {exterior angles}
 
therefore the triangles are congruent by AAA property. 
=> QR= QC .....(3)
similarily triangle PQR is congruent to triangle PBQ  and as well congruent to triangle QCR
=> QC = QR = PB        {using 3}
also QR = PQ     {of triangle QCR and triangle PBQ } ......(4)
 
 
 
now eq 4 suggests that in triangle PQR PQ = QR 
therefore triangle PQR is issoceles triangle 
=> angle a = angle b .....(5)      {angles of the issoceles triangles                                                   are equal  }
 
Now in triangle PQR
90 + angle a+ angle b = 180   
angle a+ angle b = 180 - 90 = 90
2 angle a = 90                 {using eq5}
=> angle a = 45 degree 
i.e angle QPR = 45 degree
Hence proved
Home Work Help