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A circle has an area of 78.5 cm². What is its radius? (Use π = 3.14) (2019)

Practice Questions

Q1
A circle has an area of 78.5 cm². What is its radius? (Use π = 3.14) (2019)
  1. 5 cm
  2. 7 cm
  3. 10 cm
  4. 12 cm

Questions & Step-by-Step Solutions

A circle has an area of 78.5 cm². What is its radius? (Use π = 3.14) (2019)
  • Step 1: Write down the formula for the area of a circle, which is Area = πr².
  • Step 2: Substitute the given area (78.5 cm²) and the value of π (3.14) into the formula: 78.5 = 3.14r².
  • Step 3: To find r², divide both sides of the equation by 3.14: r² = 78.5 / 3.14.
  • Step 4: Calculate the division: r² = 25.
  • Step 5: To find the radius (r), take the square root of r²: r = √25.
  • Step 6: Calculate the square root: r = 5 cm.
  • Area of a Circle – The area of a circle is calculated using the formula A = πr², where A is the area and r is the radius.
  • Solving for Radius – To find the radius from the area, rearranging the formula to r = √(A/π) is necessary.
  • Use of π – Understanding the approximation of π (3.14) is crucial for accurate calculations.
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