Function tangent_line_circle 

pub fn tangent_line_circle(
    a: &PointExpr,
    b: &PointExpr,
    c: &PointExpr,
    r: Expr,
    side: f64,
    scale: f64,
) -> Vec<Row>

Line a → b tangent to circle (c, r); side (±1) keeps the circle on its current side of the line.