The trisect of (x1,y1) and (x2, y2) is (x', y') and (x'', y'') such that

x' = (x1 + 2x2)/3

y' = (y1 + 2y2)/3

x'' = (2x1 + x2)/3

y'' = (2y1 + y2)/3

In our case x1 = -2, y1 = 3, x2 = 7, y2 = 1

x' = (-2 + 2*7)/3 = 4

y' = (3 + 2*1)/3 = 5/3

x'' = (2*(-2) + 7))/3 = 1

y'' = (2*3 + 1)/3 = 7/3

The trisect of (-2,3) and (7, 1) is (4, 5/3) and (1, 7/3).