\frac{1}{2}\times \sqrt{\left(4-0\right)^2+\left(1-0\right)^2}\times \sqrt{\left(-2-0\right)^2+\left(8-0\right)^2}
\frac{1}{2}\times \sqrt{\left(4-0\right)^2+\left(1-0\right)^2}\times \sqrt{\left(-2-0\right)^2+\left(8-0\right)^2} = \frac{1}{2}\times \sqrt{(4)^2+(1)^2}\times \sqrt{(-2)^2+(8)^2} = \frac{1}{2}\times \sqrt{16+1}\times \sqrt{4+64} = \frac{1}{2}\times \sqrt{17}\times \sqrt{68} = \frac{1}{2}\times \sqrt{17}\times \sqrt{4}\times \sqrt{17} = \frac{1}{2}\times 2\sqrt{17}\times \sqrt{17} = \sqrt{17}\times \sqrt{17} = 17.
