Plane Geometry
-  In a triangle ABC, AB + BC = 12 cm, BC + CA = 14 cm and CA + AB = 18 cm. Find the radius of the circle (in cm) which has the same perimeter as the triangle.
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                        View Hint View Answer Discuss in Forum Given that , AB + BC = 12 
 BC + CA = 14
 CA + AB = 18
 On adding , we get
 ∴ 2(AB + BC + CA) = 12 + 14 + 18 = 44
 ⇒ AB + BC + CA = 22
 ∴ 2πr = 22⇒ 2 × 22 × r = 22 7 
 Correct Option: BGiven that , AB + BC = 12 
 BC + CA = 14
 CA + AB = 18
 On adding , we get
 ∴ 2(AB + BC + CA) = 12 + 14 + 18 = 44
 ⇒ AB + BC + CA = 22
 ∴ 2πr = 22⇒ 2 × 22 × r = 22 7 ⇒ r = 7 cm 2 
-  If I be the incentre of ∆ ABC and ∠B = 70° and ∠C = 50°, then the magnitude of ∠BIC is
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                        View Hint View Answer Discuss in Forum Firstly , We draw a figure of triangle ABC whose I is incentre ,  
 Here , ∠B = 70° and ∠C = 50°∠IBC = 70° = 35° ; 2 ∠ICB = 50° = 25° ; 2 
 Correct Option: CFirstly , We draw a figure of triangle ABC whose I is incentre ,  
 Here , ∠B = 70° and ∠C = 50°∠IBC = 70° = 35° ; 2 ∠ICB = 50° = 25° ; 2 
 We know that , ∠BIC + ∠ICB + ∠IBC = 180°
 ∴ ∠BIC = 180° – 35° – 25°
 ∠BIC = 180° – 60° = 120°
-  For a triangle ABC, D, E, F are the mid-points of its sides. If ∆ABC = 24 sq. units then ∆DEF is
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                        View Hint View Answer Discuss in Forum On the basis of given in question , we draw a figure triangle ABC ,  
 Here , ∆ABC = 24 sq. units
 From figure , we have∆DEF = 1 ∆ ABC 4 
 Correct Option: BOn the basis of given in question , we draw a figure triangle ABC ,  
 Here , ∆ABC = 24 sq. units
 From figure , we have∆DEF = 1 ∆ ABC 4 ∆DEF = 1 × 24 = 6 Sq. unit 4 
-  Angle between sss ∠B is
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                        View Hint View Answer Discuss in Forum As per the given in question , we draw a figure of triangle ABC  
 ∠BPC = 120°
 ∴ ∠PBC + ∠PCB = 180°– 120°= 60°Correct Option: DAs per the given in question , we draw a figure of triangle ABC  
 ∠BPC = 120°
 ∴ ∠PBC + ∠PCB = 180°– 120°= 60°
 ∴ ∠ABC + ∠ACB = 2 × 60° = 120°
 ∴ ∠A = 180 – 120 = 60°
-  In a ∆ABC, ∠A + ∠B = 70° and ∠B + ∠C = 130°, value of ∠A is
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                        View Hint View Answer Discuss in Forum In ∆ ABC, 
 As we know that , ∠A + ∠B + ∠C = 180°
 Given , ∠A + ∠B = 70° and ∠B + ∠C = 130°Correct Option: BIn ∆ ABC, 
 As we know that , ∠A + ∠B + ∠C = 180°
 Given , ∠A + ∠B = 70° and ∠B + ∠C = 130°
 ∴ ∠A = (∠A + ∠B + ∠C) – (∠B + ∠C)
 ∠A = 180– 130°= 50°
 
	