Line Through Intersection Perpendicular to a Given Line

Line Through Intersection Perpendicular to a Given Line

## Formula

If the required line belongs to:

$$L_1+\lambda L_2=0$$

and must be perpendicular to:

$$Ax+By+C=0$$

then its coefficients must satisfy:

$$AA'+BB'=0$$

where $$A'$$ and $$B'$$ are the coefficients of $$x$$ and $$y$$ in the required line.

## Usage

- Used to select a perpendicular line from a family of lines.