Calculate the angles a12, a23, a31 of a triangle from the lengths l1, l2 and l3
the first length of the triangle
the second length of the triangle
the third length of the triangle
the level of check
the three angles a12, a23, a31 of the triangle + string-for-log
Calculate the angles a12, a23, a31 of a triangle from the lengths l1, l2 and l3