"Aire de OACB" = bar("OA") xx bar("HB") = |det(vec(a),vec(b))| = |vec(a) ^^ vec(b)|
"avec "
vec(a)((a_x),(a_y)) = vec("OA")
vec(b)((b_x),(b_y)) = vec("OB")
"H : projection orthogonale de B sur la direction de " vec("OA")
det(vec(a),vec(b)) = |(a_x,b_x),(a_y,b_y)| = a_x b_y - a_y b_x