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avatar+238 

in the figure ,central angle BAC is 30 degrees. If circle A has a diamter of 6 units , what is the area of the shaded segment 

 Oct 8, 2014

Best Answer 

 #2
avatar+23252 
+10

This can be done by first calculating the whole "slice" of the circle and then subtracting the area of the triangle.

Since there are 360° in a triangle and the central angle is 30°, the area of the slice will be 30/360 or 1/12 of the circle.

The formula for the area of a circle = πr².  

Since the diameter is 6, the radius will be 3 and the area of the circle = π·3², which is 9π.) = The area of the slice will be (1/12) of 9π which is (3/4)π .

The area of the triangle can be found various ways. One way is to use the formula:  A = .5·a·b·sinC.

a = 3     b = 3    sin(30°) = 0.5                    A = .5·3·3·.5  =  2.25

Area of the shaded area  =  (3/4)π - 2.25

 Oct 8, 2014
 #1
avatar+238 
+5

This is a kind of ACt pratice problem in Mississippi ACT Exam Prep workbook. Accctually, the triangle ABC has a height of 1.5 units.But i think it can not be,becasue the height of the triangle ABC should be shorter than the radius.And the area of the triangle ABC is 2.25 units square.So the base of the triangle ABC is 3 units.I am wondering how they get 3.I put the problem into the forum because i think they did wrong on this problem. And  i want to find ot the anwser togerther.

 Oct 8, 2014
 #2
avatar+23252 
+10
Best Answer

This can be done by first calculating the whole "slice" of the circle and then subtracting the area of the triangle.

Since there are 360° in a triangle and the central angle is 30°, the area of the slice will be 30/360 or 1/12 of the circle.

The formula for the area of a circle = πr².  

Since the diameter is 6, the radius will be 3 and the area of the circle = π·3², which is 9π.) = The area of the slice will be (1/12) of 9π which is (3/4)π .

The area of the triangle can be found various ways. One way is to use the formula:  A = .5·a·b·sinC.

a = 3     b = 3    sin(30°) = 0.5                    A = .5·3·3·.5  =  2.25

Area of the shaded area  =  (3/4)π - 2.25

geno3141 Oct 8, 2014
 #3
avatar+238 
0

i missunderstood the word "diameter".I got it now.

Thank you,geno3141.

 Oct 8, 2014

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