The given plane is x + y + z = 1 ...(1)Direction ratios of the normal to the plane are < 1, 1, 1 >∴ Direction cosines of the normal to the plane are $\langle \frac{1}{\sqrt{3}}, \frac{1}{\sqrt{3}}, \frac{1}{\sqrt{3}} \rangle$And distance of (1) from the origin $=\frac{\left|0+0+0-1\right|}{\sqrt{1+1+1}}=\frac{1}{\sqrt{3}}$