Using vector to find the positive and negative cosine value of a dihedral angle in solid geometry Cosine has positive and negative, so when I calculate two normal vectors, I set their Z values to be positive and negative. Can I guarantee that the sign of the result is correct if I calculate them all the time?

Using vector to find the positive and negative cosine value of a dihedral angle in solid geometry Cosine has positive and negative, so when I calculate two normal vectors, I set their Z values to be positive and negative. Can I guarantee that the sign of the result is correct if I calculate them all the time?

The angle between the two normal vectors may be the size of the dihedral angle of the two planes, or the complementary angle of the two dihedral angles

High school solid geometry and vector problems. I use the method of space vector to find the cosine value of the angle formed by the straight line of different planes in geometry. The calculation is negative. I am sure the calculation result is correct. But the angle formed by the straight line of different planes is within the range of 0 to 90 degrees. What if the cosine value is negative? Can I take the absolute value directly?

Yes, because the angle is in the range of (0,90), the cosine value is positive