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

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