AREA OF CIRCLES. MG 1.1 Understand the concept of a constant such as π; know the formulas for the...
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Transcript of AREA OF CIRCLES. MG 1.1 Understand the concept of a constant such as π; know the formulas for the...
AREA OF CIRCLES
• MG 1.1 Understand the concept of a constant such as π; know the formulas for the circumference and area of a circle.
• Objective: Understand how the area formula for circles is related to the area formula for parallelograms
• Learning target: Answer at least 3 of the 4 area of a circle questions correctly on the exit ticket.
• What is the formula for area of a parallelogram?
• How can we turn a circle into a parallelogram?
• Area of a parallelogram = base × height
• Area of circle parallelogram = base × height• Area of circle parallelogram = πr × r• Area of circle parallelogram = π × r²
• What is the formula for the area of a circle?
• Area of a circle = π×radius²• Remember, the exponent of 2 means to
multiply the radius by itself, NOT by the number 2.
• 5² = 5×5 = 25, NOT 5×2
• What is the area of this circle?
• Area = π × radius²• A = π × (4 m)²• A = π × 4 m × 4 m• A = 16π meters²
Answering using iPads• Open up Safari in your iPad• Go to www.m.socrative.com• For the Room Number, type in: MrPMath• Click “Join Room”• Wait for more instructions!
• What is the area of this circle?
• Area = π × radius²• A = π × (3 ft)²• A = π × 3 ft × 3 ft• A = 9π ft²
• What is the area of this circle?
• Area = π × radius²• A = π × (6 in)²• A = π × 6 in × 6 in• A = 36π in²
• What is the area of this circle? Use 3.14 for π.
• Area = π × radius²• A = π × (1 km)²• A = π × 1 km × 1 km• A = 1π km² • A = 1 × 3.14 km²• A = 3.14 km²
• How do we find the area of a circle when we only know the diameter?
• Divide the diameter by 2 to find the length of the radius.
• Use the same formula as before:Area = π × radius²
• What is the area of this circle?
• Diameter = 14 cm• Radius = 14÷2 = 7 cm• Area = π × radius²• A = π × (7 cm )²• A = π × 7 cm × 7 cm • A = 49π cm²
• What is the area of this circle?
• Diameter = 22 yd• Radius = 22 ÷ 2 = 11 yd• Area = π × radius²• A = π × (11 yd)²• A = π × 11 yd × 11 yd• A = 121π yd²
• What is the area of this circle? Use 3.14 for π.
• Diameter = 6 m• Radius = 6 ÷ 2 = 3 m• Area = π × radius²• A = π × (3 m)²• A = π × 3 m × 3 m• A = 9π m² • A = 9 ×3.14 m²• A = 28.26 m²
Direct Station• We will use the whiteboards to practice area of circle
problems.
Collaborative Station: Fill in the Table• For each circle, one piece of information will be given to
you: either the circle’s radius, diameter, circumference, or area.
• Work with your partner to fill in the other 3 pieces of information
• Example:Radius Diameter Circumference Area
Circle 1 4 cm8 cm 8π cm =
25.12 cm16π cm² = 50.24 cm²
Independent Station• Continue ST Math’s unit on area and perimeter