Find the coordinates of the circumcenter of triangle abc with vertices a(1,4) b(1,2) and c(6,2) a. 5,2 b. 3,4 c. 2.5,1 d. 3.5,3

(3.5, 3) is the circumcenter of triangle ABC. The circumcenter of a triangle is the intersection of the perpendicular bisectors of each side. All three of these perpendicular bisectors will intersect at the same point. So you have a nice self check to make sure your math is correct. Now let's calculate the equation for these bisectors. Line segment AB: Slope (4-2)/(1-1) = 2/0 = infinity. This line segment is perfectly vertical. So the bisector will be perfectly horizontal, and will pass through ((1+1)/2, (4+2)/2) = (2/2, 6/2) = (1,3). So the equation for this perpendicular bisector is y = 3. Line segment BC (2-2)/(6-1) = 0/5 = 0 This line segment is perfectly horizontal. So the bisector will be perfectly vertical, and will pass through ((1+6)/2,(2+2)/2) = (7/2, 4/2) = (3.5, 2) So the equation for this perpendicular bisector is x=3.5 So those two bisectors will intersect at point (3.5,3) which is the circumcenter of triangle ABC. Now let's do a cross check to make sure that's correct. Line segment AC Slope = (4-2)/(1-6) = 2/-5 = -2/5 The perpendicular will have slope 5/2 = 2.5. So the equation is of the form y = 2.5*x + b And will pass through the point ((1+6)/2, (4+2)/2) = (7/2, 6/2) = (3.5, 3) Plug in those coordinates and calculate b. y = 2.5x + b 3 = 2.5*3.5 + b 3 = 8.75 + b -5.75 = b So the equation for the 3rd bisector is y = 2.5x - 5.75 Now let's check if the intersection with this line against the other 2 works. Determining intersection between bisector of AC and AB y = 2.5x - 5.75 y = 3 3 = 2.5x - 5.75 8.75 = 2.5x 3.5 = x And we get the correct value. Now to check AC and BC y = 2.5x - 5.75 x = 3.5 y = 2.5*3.5 - 5.75 y = 8.75 - 5.75 y = 3 And we still get the correct intersection.