Plane Geometry
-  If P and Q are the mid points of the sides CA and GB respectively of a triangle ABC, right-angled at C. Then the value of 4 (AQ2 + BP2) is equal to :
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                        View Hint View Answer Discuss in Forum From given figure , we have 
 AQ2 = AC2 + QC2
 BP2 = BC2 + CP2
 AQ2 + BP2 = (AC2 + BC2) + (QC2 + CP2) = AB2 + PQ2.∴ AQ2 + BP2 = AB2 +  1 AB  ×  1 AB   ∵ PQ = 1 AB  2 2 2 AQ2 + BP2 = 5 AB2 ⇒ 4(AQ2 + BP2) = 5AB2 4   Correct Option: BFrom given figure , we have 
 AQ2 = AC2 + QC2
 BP2 = BC2 + CP2
 AQ2 + BP2 = (AC2 + BC2) + (QC2 + CP2) = AB2 + PQ2.∴ AQ2 + BP2 = AB2 +  1 AB  ×  1 AB   ∵ PQ = 1 AB  2 2 2 AQ2 + BP2 = 5 AB2 ⇒ 4(AQ2 + BP2) = 5AB2 4   
-  In a triangle ABC, ∠A = x°, ∠B = y° and ∠C = (y + 20)°. If 4x – y = 10, then the triangle is :
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                        View Hint View Answer Discuss in Forum Given :- ∠A = x° , ∠B = y° , ∠C = ( y + 20 )° and 4x – y = 10 
 We know that , ∠A + ∠B + ∠C = 180°
 ⇒ x + y + ( y + 20 ) = 180°
 ⇒ x + 2y = 180 - 20 = 160° ........... ( ⅰ )
 4x – y = 10 ........... ( ⅱ )
 From ( ⅰ ) and ( ⅱ ) , we get
 ⇒ y = 70 , x = 20
 ∴ The angles of the triangle are 20° , 70° , 90° .
 Hence , the triangle will be Right-angle triangle .Correct Option: AGiven :- ∠A = x° , ∠B = y° , ∠C = ( y + 20 )° and 4x – y = 10 
 We know that , ∠A + ∠B + ∠C = 180°
 ⇒ x + y + ( y + 20 ) = 180°
 ⇒ x + 2y = 180 - 20 = 160° ........... ( ⅰ )
 4x – y = 10 ........... ( ⅱ )
 From ( ⅰ ) and ( ⅱ ) , we get
 ⇒ y = 70 , x = 20
 ∴ The angles of the triangle are 20° , 70° , 90° .
 Hence , the triangle will be Right-angle triangle .
-  In a circular lawn, there is a 16 m long path in the form of a chord. If the path is 6 m away from the center of the lawn, then find the radius of the circular lawn.
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                        View Hint View Answer Discuss in Forum From given figure , we can see that 
 Let AB = 16 m , OM = 6 m , AM = BM = 8 m and OA = r
 In triangle AMO ,
 By pythagoras theorem ,
 OA2 = AM2 + OM2Correct Option: CFrom given figure , we can see that 
 Let AB = 16 m , OM = 6 m , AM = BM = 8 m and OA = r
 In triangle AMO ,
 By pythagoras theorem ,
 OA2 = AM2 + OM2
 OA2 = 82 + 62 = 64 + 36
 OA2 = 100 ⇒ OA = √ 100 = 10
 ∴ OA = r = 10 m
 The radius of the circular lawn = 10 m  
-  Of all the chords of a circle passing through a given point in it, the smallest is that which :
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                        View Hint View Answer Discuss in Forum Let C(O, r) is a circle and let M is a point within it where O is the centre and r is the radius of the circle. 
 Let CD is another chord passes through point M.
 We have to prove that AB < CD.
 Now join OM and draw OL perpendicular to CD.
 In right angle triangle OLM,
 OM is the hypotenuse.
 So OM > OLCorrect Option: DLet C(O, r) is a circle and let M is a point within it where O is the centre and r is the radius of the circle. 
 Let CD is another chord passes through point M.
 We have to prove that AB < CD.
 Now join OM and draw OL perpendicular to CD.
 In right angle triangle OLM,
 OM is the hypotenuse.
 So OM > OL
 ⇒ chord CD is nearer to O in comparison to AB.
 ⇒ CD > AB
 ⇒ AB < CD
 So all chords of a circle of a circle at a given point within it, the smallest is one which is bisected at that point.
 Hence required answer will be option D .
-  ABCD is a parallelogram and X, Y are the mid-points of sides AB and CD respectively. Then quadrilateral AXCY is a :  
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                        View Hint View Answer Discuss in Forum ABCD is a parallelogram and AXCY is a quadrilateral . 
 Since X and Y are the mid-points of AB and DC respectively.∴ AX = 1 AB and CY = 1 DC 2 2 Correct Option: AABCD is a parallelogram and AXCY is a quadrilateral . 
 Since X and Y are the mid-points of AB and DC respectively.∴ AX = 1 AB and CY = 1 DC 2 2 But ∴ AB = DC ⇒ 1 AB = 1 DC ⇒ AX = CY 2 2 
 Also, AB || DC [∴ ABCD is a parallelogram]
 ⇒ AX || YC
 Thus, in quadrilateral AXCY,
 AX || YC and AX = YC
 Hence, quadrilateral AXCY is a parallelogram.In which the opposite sides are equal and parallel.
 
	