A triangle with vertices A(-2,_1), B(-1, 4), and C(5, 0) is rotated 90 degrees counter-clockwise about vertex B. Find the co-cordinates of the image of vertex A.

neurolover25
Feb 24, 2018

#1**+1 **

There may be other ways to do this, but....one way is to position B at the origin and position the other points accordingly

So A becomes ( -2 + 1, 1 - 4) = ( - 1, - 3)

And C becomes ( 5 + 1, 0 - 4) = (6, - 4)

The slope of A from the origin is ( -3/ -1) = (3/1)

Rotated 90° counter-clockwise produces (-1/3) = (-3, 1)

The slope of C from the origin produces ( -4/6)

Rotated 90° counter=clockwise prouduces ( 6/4) = (6, 4)

So......re-positioning the points, we have

B = ( -1 , 4)

A = ( -3- 1, 1 + 4) = ( -4, 5)

C = (6 - 1, 4 + 4) = ( 5, 8)

CPhill
Feb 24, 2018