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mertymertcan

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{1 - (x^2)/4 + (x^4)/64 - (x^6)/2304 + ... }^-2 = {1 + (x^2)/2 + (x^6)/32 + ...}

the part that i didnt understand how can someone conver minus 2 power into right hand side:S. please help me, is there a general formula for this?