Points #(2 ,4 )# and #(4 ,1 )# are #(3 pi)/4 # radians apart on a circle. What is the shortest arc length between the points?
1 Answer
Explanation:
Let the radius of the circle be
We denote the center of the circle as
The line segment from
Consider the triangle formed by
#sqrt{R^2+R^2-2(R)(R)cos({3pi}/4)} #
#= sqrt2 R sqrt{1-cos({3pi}/4)}#
#= sqrt2 R sqrt{1-sqrt2/2}#
#= sqrt2 R sqrt{2-sqrt2}/sqrt2#
#= sqrt{2-sqrt2}R#
We can also use Pythagorean Theorem to find the exact length between
#sqrt((4-2)^2 + (1-4)^2) = sqrt13#
To find
#sqrt{2-sqrt2}R = sqrt13#
Solving the above equation gives
#R = sqrt{frac{13}{2-sqrt2}}#
# = sqrt{frac{13(2+sqrt2)}{(2-sqrt2)(2+sqrt2)}}#
# = sqrt{frac{13(2+sqrt2)}{2}}#
The arc length is given by
#R((3pi)/4) = sqrt{frac{13(2+sqrt2)}{2}}((3pi)/4)#