College

Select the correct answer.

Points [tex] A [/tex] and [tex] B [/tex] lie on a circle centered at point [tex] O [/tex]. If [tex] OA = 5 [/tex] and [tex] \frac{\text{length of } \widehat{AB}}{\text{circumference}} = \frac{1}{4} [/tex], what is the area of sector [tex] AOB [/tex]? Use the value [tex] \pi = 3.14 [/tex], and choose the closest answer.

A. 19.6 square units
B. 39.3 square units
C. 7.85 square units
D. 15.7 square units

Answer :

To find the area of the sector [tex]\( AOB \)[/tex] of the circle, follow these steps:

1. Identify the Radius of the Circle:
The circle has a radius, [tex]\( OA = 5 \)[/tex].

2. Find the Circumference of the Circle:
The formula for the circumference of a circle is [tex]\( C = 2\pi r \)[/tex].
So, using [tex]\(\pi = 3.14\)[/tex] and [tex]\(r = 5\)[/tex], we have:
[tex]\[
C = 2 \times 3.14 \times 5 = 31.4
\][/tex]

3. Determine the Arc Length Ratio:
The ratio of the length of arc [tex]\( \widehat{AB} \)[/tex] to the circle’s circumference is [tex]\( \frac{1}{4} \)[/tex]. This means that the arc length of [tex]\( \widehat{AB} \)[/tex] is one-fourth of the circumference of the circle.

4. Calculate the Area of the Circle:
The formula for the area of a circle is [tex]\( A = \pi r^2 \)[/tex].
So, substituting in the values, we have:
[tex]\[
A = 3.14 \times 5^2 = 3.14 \times 25 = 78.5
\][/tex]

5. Calculate the Area of Sector [tex]\( AOB \)[/tex]:
Since the arc [tex]\( \widehat{AB} \)[/tex] corresponds to [tex]\(\frac{1}{4}\)[/tex] of the circle, the area of sector [tex]\( AOB \)[/tex] is also [tex]\(\frac{1}{4}\)[/tex] of the total area of the circle.
[tex]\[
\text{Area of sector } AOB = \frac{1}{4} \times 78.5 = 19.625
\][/tex]

After the calculations, we find that the area of sector [tex]\( AOB \)[/tex] is approximately [tex]\( 19.6 \)[/tex] square units. Therefore, the closest answer is:
- A. 19.6 square units

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