It is known that the side edge and the bottom edge of the triangular prism abc-a1b1c1 are equal, and the projection of A1 in the ground ABC is the center of ABC, What is the cosine of AB and CC1
Make a1h ⊥ plane ABC, h is the outer center of △ ABC, connect ch, extend intersection AB to D, connect a1d,
Let the length of each edge be one unit,
ABC is positive,
Since h is the outer center of an equilateral triangle, then CD is the center line, the bisector and the height,
CD ⊥ AB, and D is the midpoint of ab,
According to the three perpendicular theorem, a1d ⊥ AB,
AD=1/2,
AA1//CC1,
So the angle between Aa1 and ab is the angle between CC1 and ab,
cos