答：(a²-2a-3)²=（-a²+2a+6）²两边开二次方得：a²-2a-3=-a²+2a+6或者a²-2a-3=-(-a²+2a+6)=a²-2a-6（不成立舍去）所以：2a²-4a-9=02(a²-2a+1)-11=02(a-1)
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