# What is the standard definition of transforms T_{1,-1} and D_2

• Mar 18th 2013, 06:47 AM
What is the standard definition of transforms T_{1,-1} and D_2
What is the standard definitions of the following transforms? I got them from a practice test for the NY Regents. The test does not include those definitions in its reference sheet.

1. $T_{1,-1}$
2. $D_2$

I need this for the following:
Triangle ABC has vertices A(5,1), B(1,4), and C(1,1). What are the coordinates of triangle A''B''C'', the image of triangle ABC following composite transformation $T_{1,-1} \circ D_2$.

Thanks.
• Mar 18th 2013, 08:10 AM
johng
Re: What is the standard definition of transforms T_{1,-1} and D_2
I'd say the NY regents need a copy editor. However, my initial guess was $T_{a,b}$ is translation by (a,b):
$T_{a,b}\> (x,y)=(x+a,y+b).$
Next guess was $D_k$ is central dilation by k about the origin:
$D_k(x,y)=(kx,ky)$

Apparently, from the answer, my guesses were "correct". Guessing games have no place in a math test.
• Mar 18th 2013, 12:14 PM