Area of triangle with vertices $$(x_1,y_1),(x_2,y_2),(x_3,y_3) = \dfrac{1}{2}\times[x_1(y_2 - y_3) + x_2(y_3 - y_1) + x_3(y_1 - y_2)]$$
Here, $$x_1 = 2, x_2 = -1, x_3 = 2$$
$$y_1 = 3, y_2 = 0, y_3 = -4$$
Therefore, Area of the triangle = $$\dfrac{1}{2}\times[2\times4+(-1)\times(-7)+2\times3]$$
$$= \dfrac{1}{2}\times(8+7+6) = \dfrac{21}{2}$$ sq.units.
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