A circle's center is at (2 ,1 )(2,1) and it passes through (6 ,1 )(6,1). What is the length of an arc covering (13pi ) /12 13π12 radians on the circle?

1 Answer
Sep 21, 2016

color(green)("arc length "= (13pi)/3)arc length =13π3

Explanation:

Let point 1 be P_1->(x_1,y_1)=(2,1)P1(x1,y1)=(2,1)

Let point 2 be P_2->(x_2,y_2)=(6,1)P2(x2,y2)=(6,1)

Let theta=(13pi)/12θ=13π12

Let the radius be rr

Then the arc length is rthetarθ
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color(blue)("Determine the value of "r)Determine the value of r

Using the fact that the line from P_1" to "P_2P1 to P2 can be considered as the hypotenuse of a triangle we apply Pythagoras

->(x_2-x_1)^2+(y_2-y_1)^2=r^2(x2x1)2+(y2y1)2=r2.

Thus:

r=sqrt((x_2-x_1)^2+(y_2-y_1)^2)r=(x2x1)2+(y2y1)2

r=sqrt((6-2)^2+(1-1)^2) =sqrt(4^2) = 4r=(62)2+(11)2=42=4
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color(blue)("Determine arc length")Determine arc length

"arc length is "rtheta -> cancel(4)^1xx(13pi)/(cancel(12)^3) =(13pi)/3