Question

Find a1 in the arithmetic sequence for which d = -3 and a17 = -38

Answer 1

a17=a1+16d=-38
a1=-38-16d
a1=-38-16(-3)
a1=10

Answer 2

a1=a=13
since a17=-83 then the formula is

ar^16 it is 16 because they start at one but our formulas exponents start at 0
-83=13*r^16

sfr do you know how to solve for r?

Answer 3

a=13 and a17=-83. => a+16d=-83
=> d=-6
now put this in the formula for the sum
S=35/2[2*13+34*-6]=-3115

Answer 4

http://en.wikipedia.org/wiki/Arithmetic_progression

Answer 5

there