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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


Sagot :

To find the area of sector [tex]\(AOB\)[/tex] in a circle with center [tex]\(O\)[/tex], where the radius [tex]\(OA = 5\)[/tex] and the ratio of the length of arc [tex]\(\widehat{AB}\)[/tex] to the circumference of the circle is [tex]\(\frac{1}{4}\)[/tex], we can follow these steps:

1. Identify the radius of the circle:
Since [tex]\(OA\)[/tex] is the radius and given that [tex]\(OA = 5\)[/tex], the radius [tex]\(r = 5\)[/tex] units.

2. Understand the given ratio:
The length of arc [tex]\(\widehat{AB}\)[/tex] is given as [tex]\(\frac{1}{4}\)[/tex] of the total circumference of the circle.

3. Find the total circumference of the circle:
The circumference [tex]\(C\)[/tex] of a circle is given by the formula:
[tex]\[ C = 2 \pi r \][/tex]
Plugging in the given values:
[tex]\[ C = 2 \times 3.14 \times 5 = 31.4 \text{ units} \][/tex]

4. Calculate the area of the complete circle:
The area [tex]\(A\)[/tex] of a circle is given by:
[tex]\[ A = \pi r^2 \][/tex]
Plugging in the given values:
[tex]\[ A = 3.14 \times (5)^2 = 78.5 \text{ square units} \][/tex]

5. Determine the area of sector [tex]\(AOB\)[/tex]:
Since the arc [tex]\(\widehat{AB}\)[/tex] spans [tex]\(\frac{1}{4}\)[/tex] of the circle's circumference, the sector also encompasses [tex]\(\frac{1}{4}\)[/tex] of the circle's area. Therefore, the area of sector [tex]\(AOB\)[/tex] is:
[tex]\[ \text{Area of sector } AOB = \frac{1}{4} \times \text{Total Area} = \frac{1}{4} \times 78.5 = 19.625 \text{ square units} \][/tex]

The closest answer to 19.625 square units, based on the options provided, is [tex]\( 19.6 \)[/tex] square units.

Thus, the correct answer is:

A. [tex]\( \text{19.6 square units} \)[/tex]