(a²-4b²/a²-4b²+a+2b)-a²+4ab-4b²
=(a+2b)(a-2b)/(a+2b)(a-2b+1)-a^2+4ab-4b^2
=(a-2b)/(a-2b+1)-(a-2b)^2
=2/(2+1)-2^2
=2/3-4
=-10/3

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