Plane Geometry
-  Suppose that the medians BD, CE and AF of a triangle ABC meet at G. Then AG : GF is
 
- 
                        View Hint View Answer Discuss in Forum We draw a figure triangle ABC whose the medians BD, CE and AFmeet at point G ,  
 Point G is the centroid of ∆ ABC.
 Point G divides AF (each median) in the ratio 2 : 1.
 Proof :- 
 Reflect ∆ ABC on side AC.
 ABCB1 is a parallelogram.
 BEB1 is a straight line. and
 ∵ CD = AD, and CD || AD1
 DCD1A is a parallelogram.
 DG || CG1Correct Option: BWe draw a figure triangle ABC whose the medians BD, CE and AFmeet at point G ,  
 Point G is the centroid of ∆ ABC.
 Point G divides AF (each median) in the ratio 2 : 1.
 Proof :- 
 Reflect ∆ ABC on side AC.
 ABCB1 is a parallelogram.
 BEB1 is a straight line. and
 ∵ CD = AD, and CD || AD1
 DCD1A is a parallelogram.
 DG || CG1
 ∵ BD = DC and DG || CG, and BG = GG1
 ∴ BG : GG1 = 1 : 1
 ∵ GE = EG1, BG = GE = 2 : 1
-  AD is the median of ∆ ABC. If O is the centroid and AO = 10 cm, then OD is
 
- 
                        View Hint View Answer Discuss in Forum We draw a figure triangle ABC whose the side AD is the median and O is the centroid ,  
 Here , AO = 10 cm
 Point O, is the centroid of ∆ ABC.
 AO : OD = 2 : 1⇒ 10 = 2 ⇒ 2 × OD = 10 OD 1 
 Correct Option: AWe draw a figure triangle ABC whose the side AD is the median and O is the centroid ,  
 Here , AO = 10 cm
 Point O, is the centroid of ∆ ABC.
 AO : OD = 2 : 1⇒ 10 = 2 ⇒ 2 × OD = 10 OD 1 ⇒ OD = 10 = 5 cm. 2 
-  Possible lengths of the three sides of a triangle are :
 
- 
                        View Hint View Answer Discuss in Forum We know that the sum of two sides of a triangle is greater than the third side. 
 Clearly,
 3 + 4 > 5
 4 + 5 > 3
 5 + 3 > 4Correct Option: BWe know that the sum of two sides of a triangle is greater than the third side. 
 Clearly,
 3 + 4 > 5
 4 + 5 > 3
 5 + 3 > 4
 Therefore , Possible lengths of the three sides of a triangle are 3 cm, 4 cm and 5 cm .
-  In ∆ ABC, AB = a – b, AC = √a² + b² and BC = √2ab, then find angle B.
- 
                        View Hint View Answer Discuss in Forum According to question , we draw a figure  
 Given , AB = a – b; BC = √2ab ;
 AC = √a² + b²
 ∴ AB² + BC² = (a – b)² + (√2ab)²Correct Option: CAccording to question , we draw a figure  
 Given , AB = a – b; BC = √2ab ;
 AC = √a² + b²
 ∴ AB² + BC² = (a – b)² + (√2ab)²
 AB² + BC² = a² + b² – 2ab + 2ab = a² + b² = AC²
 ∴ ∠ABC = 90°
-  BD and CE are two medians of the triangle ABC. If EO = 7cm, then the length of CE is 
- 
                        View Hint View Answer Discuss in Forum  
 Given that , EO = 7cm,
 Point ‘O’ is the centroid of triangle ABC.∴ OE = 1 CE 3 
 Correct Option: C 
 Given that , EO = 7cm,
 Point ‘O’ is the centroid of triangle ABC.∴ OE = 1 CE 3 ⇒ 7 = 1 CE 3 
 ∴ CE = 7 × 3 = 21 cm
 
	