Question 1035616
Write the expression below in expanded form and then find the sum:

3
Σ   (4^k-1)
k=1 
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Sub 1 for k: --> 4^0 = 1
etc
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1 + 4 + 16 = 21
1 + 3 + 9 + 27 = 40
1 + 1/4 + 1/16 = 21/16
4 + 16 + 64 = 84