Download - Circles g7
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Circles
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What is the circle?
• The set of all points those are equidistant from a fixed point is called a circle.
• The fixed is called center of the circle.• The line segment between two points on the
circle which is passing through the center is called the diameter.
• The line segment between any point on the circle and the center is called the radius (plural radii).
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circle
The fixed point(center)
diameterradius
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Circumference:
• The circumference is the length of the outer boundary of a circle.
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Finding the circumference
• The circumference of a circle is given by the formula C = πD, where C is the circumference and D is the diameter of a circle.
• Notice that D = 2xRadius = 2r• π : an irrational number which is
approximately equal to 3.14.
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Example:
• Find the circumference of each of the following circles.
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Find the circumference of each of these circles.
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Find the perimeter of each of the shapes below. (Remember to add the lengths of the straight sections.)
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A scooter tire has a diameter of 32 cm. What is the perimeter of the tire?
Find the circumference of the Ferris wheel shown below.
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Area of a circleIf the circle is divided into smaller sectors, the curved sides of the sectors become straighter and, hence, the shape is closer to a perfect rectangle.
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Finding the area of a circle
• The area of a circle, A, can be found using the formula A = π r2 , where π is a constant with a value of approximately 3.14 and r is the radius of the circle.
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Example:
• Find the area of each of the following circles.
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Find the area of each of these circles.
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Find the area of each of the shapes below.
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Definition: An annulus (plural annuli) is the shape formed between two circles with a common center (called concentric circles).
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Find the area of the annulus for the following sets of concentric circles.
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Find the area of the following shapes: