Chapter F - Foundations: A Prelude to Functions - Section F.1 The Distance and Midpoint Formulas - F.1 Assess Your Understanding - Page 7: 34

See graph. $AC^2=AB^2+BC^2$, $4\ unit^2$.

Step 1. See graph. Step 2. $AB=\sqrt {(4-4)^2+(-3-1)^2}=4$, $BC=\sqrt {(4-2)^2+(1-1)^2}=2$, $AC=\sqrt {(4-2)^2+(-3-1)^2}=\sqrt {20}$, Step 3. Check $AC^2=AB^2+BC^2$, thus it is a right triangle, Step 4. $Area=\frac{1}{2}(4)(2)=4\ unit^2$.