a) Có $x_{E} = \frac{x_{M} + x_{N}}{2} = \frac{3 + 7}{2} = 5$
$y_{E} = \frac{y_{M} + y_{N}}{2} = \frac{3 + 3}{2} = 3$
Vậy E(5; 3)
b) Có $x_{G} = \frac{x_{M} + x_{N} + x_{P}}{3} = \frac{3 + 7 + 3}{3} = \frac{13}{3}$
$Y_{G} = \frac{y_{M} + y_{N} + y_{P}}{3} = \frac{3 + 3 + }{3} = \frac{13}{3}$
Vậy G$(\frac{13}{3}; \frac{13}{3})$