Plane Geometry
- In the given figure, side BC of Δ ABC is produced to form ray BD and CE || BA. Then ∠ ACD is equal to :
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From above given figure , we can see that
CE || BA and AC is the transversal.
∴ ∠4 = ∠1 (alternate interior ∠s) .......... ( 1 )
Again, CE || BA and BD is the transversal.
∴ ∠5 = ∠2 (corresponding ∠s) ................( 2 )Correct Option: C
From above given figure , we can see that
CE || BA and AC is the transversal.
∴ ∠4 = ∠1 (alternate interior ∠s) .......... ( 1 )
Again, CE || BA and BD is the transversal.
∴ ∠5 = ∠2 (corresponding ∠s) ................( 2 )
Adding equations ( 1 ) and ( 2 )
∴ ∠4 + ∠5 = ∠1 + ∠2
∴∠ACD = ∠A + ∠B.
- In fig, AB = AC, D is a point on AC and E on AB such that AD = ED = EC = BC. Then ∠A : ∠B :
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As per given figure , we can see that
In ΔBCE, BC = EC, ∴ ∠B = ∠BEC
In ΔCDE, ED = EC, ∴ ∠ECD = ∠EDC
and In ΔADE, AD = ED, ∴ ∠AED = ∠A
Now ∠B = ∠BEC = ∠A + ∠ECD = ∠A + ∠EDC = ∠A + ∠EAD + ∠AED
{ ∴ ∠EDC = ∠EAD + ∠AED }
=∠A + ∠A + ∠A = 3∠A { By ASA property }Correct Option: D
As per given figure , we can see that
In ΔBCE, BC = EC, ∴ ∠B = ∠BEC
In ΔCDE, ED = EC, ∴ ∠ECD = ∠EDC
and In ΔADE, AD = ED, ∴ ∠AED = ∠A
Now ∠B = ∠BEC = ∠A + ∠ECD = ∠A + ∠EDC = ∠A + ∠EAD + ∠AED
{ ∴ ∠EDC = ∠EAD + ∠AED }
=∠A + ∠A + ∠A = 3∠A { By ASA property }∴ ∠B = ∠3 ∠A 1
⇒ ∠A : ∠B = 1 : 3.
- PQRS is a square. The ∠ SRP is equal to :
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PQRS is a square .
We know that Every angle of square is 90° and the diagonals bisect each other at right angles .
SP = SR and ∠S = 90°Correct Option: A
PQRS is a square .
We know that Every angle of square is 90° and the diagonals bisect each other at right angles .
SP = SR and ∠S = 90°and ∠SRP = ∠SPR = 1 (90°) = 45° 2
Hence, ∠SRP = 45°.
- The two sides of a right triangle containing the right angle measure 3 cm and 4 cm. The radius of the in circle of the triangle is :
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If the in circle of a triangle ABC touches BC at D, then |BC - CD| = |AB - AC|
In our case, AC = 5, AB = 3
⇒ AC – AB = 2
∴ CD – BD = 2
Correct Option: C
First method :-
If the in circle of a triangle ABC touches BC at D, then |BC - CD| = |AB - AC|
In our case, AC = 5, AB = 3
⇒ AC – AB = 2
∴ CD – BD = 2
In our case, BC = 4
⇒ BD + BD = 4 and – BD + DC = 22
⇒ CD = 3
⇒ BD = 1 = OE = Radius of the in circle.
second method :-
We know that , In right angle triangle
Here , a = 3 cm , b = 4 cm and c = 5 cm
We know that ,The radius of the incircle = a + b - c 2 The radius of the incircle = 3 + 4 - 5 = 2 2 2
∴ The radius of the incircle = 1 cm
- If one of the diagonals of a rhombus is equal to its side, then the diagonals of the rhombus are in the ratio :
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Let ABCD is a rhombus in which AB = BC = CD = DA = diagonal CA.
In triangle ABC ,
AB = BC = CA , therefore ∠B = 60°
∠D = ∠B = 60°
∠A=180 - ∠B = 180° - 60° =120°
∠C = ∠A=120°
Hence ,The ratio of diagonals = √2 : 1Correct Option: B
Let ABCD is a rhombus in which AB = BC = CD = DA = diagonal CA.
In triangle ABC ,
AB = BC = CA , therefore ∠B = 60°
∠D = ∠B = 60°
∠A=180 - ∠B = 180° - 60° =120°
∠C = ∠A=120°
Hence ,The ratio of diagonals = √2 : 1