G-C Geometry—Circles: Area of Minor Segment

Find the area of the shaded region when ∠AOB is 90 degrees and the radius is 2 .

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Step 1 of 5

To solve the problem, we first find the height and width of the inscribed triangle.

To calculate the measure of ∠OBA , we draw a perpendicular line from the center to chord AB , which bisects the chord.



Height of triangle △OBA = radius sin ( ∠OBA )

AB 2 or half base width of the triangle △OBA = radius cos ( ∠OBA )

The measure of ∠OBA is calculated as 180 - ( 90 + 90 2 ) degrees. One angle is 90 degrees because the perpendicular line from the center to chord AB also bisects ∠AOB .

Step 2 of 5

The height of the triangle is 2 sin ( 180 - ( 90 + 90 2 ) ) = 2 .

Half the triangle width is 2 cos ( 180 - ( 90 + 90 2 ) ) = 2 .

Therefore, the full width of the triangle is 2 2 = 2 2 .

Step 3 of 5

Now, we calculate the area of triangle △OBA , which is given by Area = 1 2 base height.

Substitute the values:

Area of triangle △OBA = 1 2 ( 2 2 ) 2 = 2

Step 4 of 5

The area of the circular sector subtended by the minor angle ∠AOB is 90 360 ( π 2 2 ) = π .

Step 5 of 5

The shaded area is obtained by subtracting the area of triangle △OBA from the area of the circular sector subtended by the minor angle ∠AOB .

Area of the shaded region = π - 2 = 1.14 (rounded to the nearest hundredth)