Plane Geometry
- In a circle with centre O, AB is a chord, and AP is a tangent to the circle. If ∠AOB = 140°, then the measure of ∠PAB is
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According to question , we draw a figure of a circle with centre O ,
In ∆ OAB,
Here , OA = OB = radius
∴ ∠OAB = ∠OBA
∴ ∠OAB + ∠OBA + ∠AOB = 180°
∴ 2∠OAB = 180° – 140° = 40°Correct Option: C
According to question , we draw a figure of a circle with centre O ,
In ∆ OAB,
Here , OA = OB = radius
∴ ∠OAB = ∠OBA
∴ ∠OAB + ∠OBA + ∠AOB = 180°
∴ 2∠OAB = 180° – 140° = 40°⇒ ∠OAB = 40 = 20° 2
∴ ∠PAO = 90°
∴ ∠PAB = 90° – 20° = 70°
- Two circles with radii 25 cm and 9 cm touch each other externally. The length of the direct common tangent is
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On the basis of question we draw a figure of two circles with radii 25 cm and 9 cm touch each other externally.
Here , r1 = 25 cm, r2 = 9 cm
We find the required answer with the help of given formula ,
Length of common tangent = √(distance between centres)² - (r1 - r2)²
Length of common tangent = √(25 + 9)² - (25 - 9)²Correct Option: B
On the basis of question we draw a figure of two circles with radii 25 cm and 9 cm touch each other externally.
Here , r1 = 25 cm, r2 = 9 cm
We find the required answer with the help of given formula ,
Length of common tangent = √(distance between centres)² - (r1 - r2)²
Length of common tangent = √(25 + 9)² - (25 - 9)²
Length of common tangent = √(34)² - (16)²
Length of common tangent = √(34 + 16)(34 - 16)
Length of common tangent = √50 × 18 = 30 cm.
- ST is a tangent to the circle at P and QR is a diameter of the circle. If ∠RPT = 50°, then the value of ∠SPQ is
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According to question , we draw a figure of a circle with centre O ,
Here , ∠RPT = 50°
∠RPQ = 90° (Angle of semi circle)Correct Option: A
According to question , we draw a figure of a circle with centre O ,
Here , ∠RPT = 50°
∠RPQ = 90° (Angle of semi circle)
∠TPS = 180°
∴ ∠SPQ = 180° – 50° – 90° = 40°
- The distance between the centres of two circles with radii 9 cm and 16 cm is 25 cm. The length of the segment of the tangent between them is
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On the basis of question we draw a figure of two circles with radii 9 cm and 16 cm ,
Given that , r1 = 9 cm and r2 = 16 cm
Distance between two centres = 25 cm
∴ Required length of tangent = √(Distance between two centres)2 - (r1 - r2)2
Required length of tangent = √(25)² - (16 -9)²Correct Option: A
On the basis of question we draw a figure of two circles with radii 9 cm and 16 cm ,
Given that , r1 = 9 cm and r2 = 16 cm
Distance between two centres = 25 cm
∴ Required length of tangent = √(Distance between two centres)2 - (r1 - r2)2
Required length of tangent = √(25)² - (16 -9)²
Required length of tangent = √625 - 49
Required length of tangent = √576 = 24 cm
- DE is a tangent to the circumcircle of ∆ ABC at the vertex A such that DE|| BC. If AB = 17 cm, then the length of AC is equalto
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As per the given in question , we draw a figure
DE || BC
∴ ∠DAB = ∠ABC
∠EAC = ∠ACBCorrect Option: D
As per the given in question , we draw a figure
DE || BC
∴ ∠DAB = ∠ABC
∠EAC = ∠ACB
Hence, ABC is equilateral triangle.
∴ side AB = AC = BC = 17 cm