# Just a variation in geometric sums

Algebra Level 3

$\large a^0 + a^1 + a^2 + \ldots + a^n = \frac{a^{n+1}-1}{a-1}$

We know that for the geometric sum above holds true. Can you find a formula for the sum

$\large a^0 + a^2 + a^4 + \ldots + a^{2n}?$

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