A triangle has corners at #(4, 6 )#, ( 1 , 7)#, and #( 3, -4)#. If the triangle is reflected across the x-axis, what will its new centroid be?

2 Answers
May 25, 2016

#(8/3,-3)#

Explanation:

The first step here is to find the coordinates of the centroid of the triangle.

Given the 3 vertices #(x_1,y_1),(x_2,y_2)" and " (x_3,y_3)#

Then the coords of the centroid are found as follows.

#color(red)(|bar(ul(color(white)(a/a)color(black)(1/3(x_1+x_2+x_3),1/3(y_1+y_2+y_3))color(white)(a/a)|)))#

here let #(x_1,y_1)=(4,6),(x_2,y_2)=(1,7),(x_3,y_3)=(3,-4)#

x-coord #=1/3(4+1+3)=8/3" #

and y-coord #=1/3(6+7-4)=3#

coords of centroid #=(8/3,3)#

now, under a reflection in the x-axis

a point (x ,y) → (x ,-y)

hence coords of centroid #(8/3,3)rArr(8/3,-3)#

May 25, 2016

New centroid is #(8/3,-3)#

Explanation:

The centroid of the triangle with corners at #(4,6)#, #(1,7)# and #(3, -4)# is

#((4+1+3)/3,(6+7+(-4))/3)# or #(8/3,3)#

When triangle is reflected across the x-axis, its centroid too is reflected across the x-axis

and as reflection of a point #(x_1,y_1)# in x-axis is #(x_1,-y_1)#,

New centroid is #(8/3,-3)#