Question : In the given figure, the length of arc AB is equal to twice the length of radius $r$ of the circle. Find the area of sector OAB in terms of the radius $r$.
Option 1: $3r$
Option 2: $2r$
Option 3: $ \pi r^2$
Option 4: $ r^2$
Correct Answer: $ r^2$
Solution : Let the radius of the circle be $r$ Here, we know that the length of the arc = $2r$ $⇒ l = r × \theta$ Where $\theta$ is in radian and $l$ is the length of the arc. $⇒ 2r = r × \theta$ $⇒ \theta = 2$ Area of the sector = $\frac{\theta}{360} \times \pi r^2$ Area of the sector = $\frac{2}{360} × 180 × r^2$ [As $\pi = 180°$] Area of the sector = $r^2$ Hence, the area of the sector OAB in terms of the radius is $r^2$. Hence, the correct answer is $r^2$.
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Question : A sector of a circle has a central angle of 45° and an arc length of 22 cm. Find the radius of the circle. ( Use $\pi=\frac{22}{7}$)
Option 1: 32 cm
Option 2: 35 cm
Option 3: 28 cm
Option 4: 36 cm
Question : The area of the sector of a circle is 128 cm2. If the length of the arc of that sector is 64 cm, then find the radius of the circle.
Option 1: 4 cm
Option 2: 8 cm
Option 3: 2 cm
Option 4: 16 cm
Question : The radius of circle A is twice that of circle B and the radius of circle B is twice that of circle C. Their area will be in the ratio:
Option 1: 16 : 4 : 1
Option 2: 4 : 2 : 1
Option 3: 1 : 2 : 4
Option 4: 1 : 4 : 16
Question : Chord PQ is the perpendicular bisector of radius OA of the circle with centre O. (A is a point on the edge of the circle). If the length of Arc $PAQ=\frac{2\pi}{3}$. What is the length of chord PQ?
Option 1: $2$
Option 2: $\sqrt{3}$
Option 3: $2\sqrt{3}$
Option 4: $1$
Question : Three equal circles of unit radius touch one another. Then the area of the circle circumscribing the three circles is:
Option 1: $6 \pi (2+ \sqrt3)^2$
Option 2: $\frac{\pi}{6} (2+ \sqrt3)^2$
Option 3: $\frac{\pi}{3} (2+ \sqrt3)^2$
Option 4: $3\pi (2+ \sqrt3)^2$
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