Calculate the length l3 and angle a12 of a triangle from a31, l1 and l2
the angle between l3 and l1 in radian
the first length of the triangle
the second length of the triangle
the level of check
the two possible sets of l3, a31, a12 of the triangle [l3a, a31a, a12a, l3b, a31b, a12b] + string-for-log
Calculate the length l3 and angle a12 of a triangle from a31, l1 and l2