The condition that the equation `lx +my +n = 0` represents the equatio of a straight line in the normal form is

Options

A. `l^(2) +m^(2)+- 0, n gt 0`
B. `l^(2) +m^(2)+-0, n lt0`
C. `l^(2)+m^(2) = 1, n lt 0`
D. `l^(2) +m^(2) = 1, n gt 0`

Answer

C

Explanation

Equation of the line in normal form is `x cos alpha +y sin alpha =p`,
`:. L = cos alpha, m = sin alpha, n =- p`
`:. l^(2) +m^(2) = 1` and `n lt 0`