How can you use the double angle or half angle formula to find cos(π/12)?

Select the quadratic that has root x = 8 and x = -5

The figure shows triangle def and line segment bc, which is parallel to ef: triangle def has a point b on side de and point c on side df. the line bc is parallel to the line ef. part a: is triangle def similar to triangle dbc? explain using what you know about triangle similarity. part b: which line segment on triangle dbc corresponds to line segment ef? explain your answer. part c: which angle on triangle dbc corresponds to angle f? explain your answer. asap

The two cones below are similar. what is the height of the smaller cone?