If a circle has an area of 78.5 cm², what is its radius?

Practice Questions

Q1
If a circle has an area of 78.5 cm², what is its radius?
  1. 5 cm
  2. 7 cm
  3. 10 cm
  4. 6 cm

Questions & Step-by-Step Solutions

If a circle has an area of 78.5 cm², what is its radius?
  • Step 1: Write down the formula for the area of a circle, which is Area = πr².
  • Step 2: We know the area is 78.5 cm², so we can set up the equation: 78.5 = πr².
  • Step 3: To find r², we need to isolate it. Divide both sides by π: r² = 78.5 / π.
  • Step 4: Now, we need to find the value of π. Use approximately 3.14 for π.
  • Step 5: Calculate 78.5 / 3.14 to find r²: r² ≈ 25.
  • Step 6: To find r, take the square root of r²: r = √25.
  • Step 7: Calculate the square root of 25, which is 5.
  • Step 8: Therefore, the radius of the circle is approximately 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.
  • Square Root Calculation – Finding the radius involves taking the square root of the area divided by π.
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