Question

What is the sum to 5 terms of the geometric progression whose first term is 54 and fourth term is 2?

Answer 1

same as before.
54(1 - 1/3^4)/(1 - 1/3)

Answer 2

a1=54 ,a4= 2
a1 + 3d =2
a1 =54
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3d = -52 d = -52/3
s5 =n/2[2a+(n-1)d] = 5/2[2x54+ 4x-52/3]
= 5/2[108-208/3] = 5/2[324-208/3] =5/2[116/3] =5x116/2x3
= 580/6 = 290/3