Question

If p is length of perpendicular from origin to the line whose intercepts on the axes are a and b, then show that `1/("p"^3) = 1/("a"^2) + 1/("b"^2)`

Answer 1

The equation of the line with x-intercept a and y-intercept b is `x/"a" + y/"b"` = 1 ......(1)

The length of the perpendicular from the origin (0, 0) to the line (1) is

p = `(1/"a" xx 0 + 1/"b" xx 0 - 1)/sqrt((1/"a")^2 + (1/"b")^2`

p = `- 1/sqrt(1/("a"^2) + 1/("b"^2)`

Since p is the length p cannot be negative.

∴ p = `1/sqrt(1/("a"^2) + 1/("b"^2)`

`1/"p" = sqrt(1/("a"^2) + 1/("b"^2)`

Squaring on both sides

`1/("p"^2) = 1/("a"^2) + 1/("b"^2)`