Question 760277
the answers are 
the first term = -68#the difference is -17

we know the sixth term is 17.  so 17 = fisrt term (a) + 5 * difference(d) (using formula for finding a term of an AP)

we know the sum of the fisrt 13 terms is 0. so 0 = 13/2 (2a + 12d).  using the formula for the sum of the fisrt n terms in an AP.

rearrange the fisrt equation to read 17-5d = a, and substitute this into the second equation and rearrange to get d= -17.

substitute this into the fisrt equation to get a=-68