. The length of is 25 feet. If the radius of the circle is 17 feet, which of the following is the nearest area of the yellow region in square feet?
The circle above has its center at point
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The yellow region is a segment of a circle. Draw O C and O D to form a sector of a circle. Apply pythagorean theorem in △ C A O .
( C A ) 2 = 1 7 2 − 8 2
( C A ) 2 = 2 2 5
C A = 2 2 5
C A = 1 5 feet
It follows that,
C D = 2 ( C A ) = 2 ( 1 5 ) = 3 0 feet
Apply cosine law in △ C D O ,
3 0 2 = 1 7 2 + 1 7 2 − 2 ( 1 7 ) ( 1 7 ) ( c o s ∠ C O D )
c o s ( ∠ C O D ) = − 2 8 9 1 6 1
∠ C O D = c o s − 1 ( − 2 8 9 1 6 1 ) ≈ 1 2 3 . 8 5 5 ∘
Calculate the area of the sector:
A s e c t o r = 3 6 0 ∠ C O D ( π ) ( r 2 ) = 3 6 0 1 2 3 . 8 5 5 ( 3 . 1 4 ) ( 1 7 2 ) ≈ 3 1 2 . 2 f t 2
Calculate the area of the triangle:
A T = 2 1 ( b ) ( h ) = 2 1 ( 3 0 ) ( 8 ) = 1 2 0 ‘ f t 2
Calculate the area of the segment:
A = A s e c t o r − A T = 3 1 2 . 2 − 1 2 0 = 1 9 2 . 2 f t 2
Based from the given options, the nearest area of the yellow region is 1 9 2 f t 2 .