Plane Geometry
- Suppose that the medians BD, CE and AF of a triangle ABC meet at G. Then AG : GF is
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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: B
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 || 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
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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: A
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 ⇒ OD = 10 = 5 cm. 2
- Possible lengths of the three sides of a triangle are :
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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: B
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 > 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.
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According to question , we draw a figure
Given , AB = a – b; BC = √2ab ;
AC = √a² + b²
∴ AB² + BC² = (a – b)² + (√2ab)²Correct Option: C
According 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
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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