hello : the common ratio is r = -95-(-100)=5 the general terme is : un= u1+(n-1)r un = -100 +(n-1)(5) un =-100 +5n-5 un = 5n-105 The last term is : 100 un =100 5n-105 = 100 5n =205 n = 41 (Number of terms) The last term is : u 41 the sum is : S= (41/2)(-100+100)=0
