i 3 + i 2 + i + 1 i 6 3 + i 6 2 + i 6 1 + … + i 3 + i 2 + i + 1 = ?
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why won't we cut out the factors
= 1 + i + i 2 + i 3 1 + i + i 2 + i 3 + i 4 … i 6 3 = 1 + i + 1 − i 1 + i + i 2 + i 3 + i 4 … i 6 3 = 0 1 + i + i 2 + i 3 + i 4 … i 6 3
Since the denominator is 0, we can immediately see that the fraction's value will be indeterminate. Hence there is no need to evaluate expression in the numerator.
It would be made much clearer if you immediately explained that the denominator is 0, hence we have an indeterminate form.
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Let x be the answer to the expression.
Factoring the terms, we get
x = ( i 2 + 1 ) ( i + 1 ) ( i 3 2 + 1 ) ( i 1 6 + 1 ) ( i 8 + 1 ) ( i 4 + 1 ) ( i 2 + 1 ) ( i + 1 )
Now, we can cancel the term i + 1 , since its nonzero, but not i 2 + 1 because it has a value of zero.
We see now that x = 0 0 .
This implies that x × 0 = 0 . Since any value of x would make the statement correct, this makes it indeterminate .
PS: x will only be undefined if x = 0 a for nonzero value of a .
Also, we cannot use L'Hopital's rule here because i is a number, and not a variable. After all, we're not looking for limits.