Find the area of 3/4 of a circle with a radius of 4.2 cm.

From the condition, we know the radius of the given circle and it is 4.2 cm. And the value of the constant of the number π = 3.1 (rounded to tenths) is also known.
In order to find the area of a circle, let’s recall the formula for finding it through the radius of the circle.
S = πR ^ 2, where R is the radius of the circle.
We just need to substitute the known values and perform the steps to find the area of the circle.
S = 3.1 * 4.2 ^ 2 = 3.1 * 17.64 = 54.684 cm2.
Now we find 3/4 of the area:
3/4 * S = 3/4 * 54.684 = 41.013 cm2.
Answer: 3/4 of the area of a circle is 41.013 cm2.

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