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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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: B
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
- In a triangle ABC, ∠A = x°, ∠B = y° and ∠C = (y + 20)°. If 4x – y = 10, then the triangle is :
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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: A
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 .
- 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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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: C
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 + 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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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: D
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 > 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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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: A
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 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.