Which is the formula for the nth partial sum of the arithmetic series with a4=36 and d=8? A Sn=n2[12+8(n−1)] B Sn=n2[12+16(n−1)] C Sn=n2[24+8(n−1)] D Sn=n2[24+16(n−1)]

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