ind the direction cosine of the tangent at point (6, 7, 8) to the conic x² + y² + z² = 1, xyz = 1.

a) (6/7, 7/8, 8/9)
b) (7/8, 8/9, 9/10)
c) (8/9, 9/10, 10/11)
d) (9/10, 10/11, 11/12)