The following problem refers to a geometric sequence:
If a_1=-2 and r=-1.Find s_28.
This the formula was given by my instructor:
S_n=a_1(1-r^n)/1-r
=-2(1-(-1)^28)/1-(-1)
=-2*2/2
=-4/2
=-2
where did I go wrong?
Can You help me correct it please.
Help me please.
1-(-1)^28 = 1-1 = 0
(-1)^28 = 1
-1 to any even power is +1