Line is $\; \frac{x}{1} = \; \frac{y}{0} = \; \frac{z}{0}$ and let point $P(2,5,7)$Direction ratios of line are <1, 0, 0>This line is x-axis.Any point on the x-axis has the general co-ordinate (x, 0, 0)For the x-axis, the foot of perpendicular is simply the x-coordinate of the point P with other co-ordinate being zero.∴ Foot of perpendicular is Q(2, 0, 0)∴ Length of the perpendicular is the distance between P(2, 5, 7) & Q(2, 0, 0)$\therefore d = \sqrt{ (x_2 - x_1)^2 + (y_2 - y_1)^2 + (z_2 z_1)^2 }$$=\sqrt{(2-2)^2+(5-0)^2+(7-0)^2}$$=\sqrt{0+25+49}$$=\sqrt{74}$