(5a²-3b²)-【(a²-2ab-b²)-(5a²-2ab-3b²)】
=5a²-3b²-【a²-2ab-b²-5a²+2ab+3b²】
=5a²-3b²-【-4a²+2b²】
=5a²-3b²+4a²-2b²
=9a²-5b²
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