Find the sum of terms
Find .
Note that the left hand side of the equation represents the sum of a geometric progression.
The answer is 18874359.
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1 solution
9 + 1 8 + 3 6 + 7 2 + . . . + 9 4 3 7 1 8 4 = x , 1 8 + 3 6 + 7 2 + 1 4 4 . . . + 1 8 8 7 4 3 6 8 = 2 x ,subtract them and get x = 1 8 8 7 4 3 6 8 − 9 = 1 8 8 7 4 5 9 (To make sure, 9 4 3 7 1 8 4 = 2 2 0 × 9 )