Geometry help please?

center of gravity of triangle SRT
= ⅓Σ[(1,2), (0,-3), (-4,3)]
= ⅓((1 + 0 + -4), (2 + -3 +3))
= (-1, ⅔)

Dilated triangle S'R'T' has the same center of gravity of triangle SRT.

S'R'T' = dilated SRT

S' = CG + (S - CG) * scaling factor
R' = CG + (R - CG) * scaling factor
T' = CG + (T - CG) * scaling factor

S'
= (-1, ⅔) + ((1, 2) - (-1, ⅔)) * 2
= (-1, ⅔) + (1 - -1, 2 - ⅔) * 2
= (-1, ⅔) + (4, 2⅔)
= (3, 3⅓)

R'
= (-1, ⅔) + ((0, -3) - (-1, ⅔)) * 2
= (-1, ⅔) + (0 - -1, -3 - ⅔) * 2
= (-1, ⅔) + (2, -7⅓)
= (1, -6⅔)

T'
= (-1, ⅔) + ((-4, 3) - (-1, ⅔)) * 2
= (-1, ⅔) + (-4 - -1, 3 - ⅔) * 2
= (-1, ⅔) + (-6, 4⅔)
= (-7, 5⅓)

Spreadsheet file visualization: http://www.webdownload.yolasite.com/resources/Book1.xls

Is the center of dilation (0, 0)?

If so, S' (2, 4), R' (0, -6), T' (-8, 6).