题目内容
已知a＞0，则(a
+a-
)2-(a
-a-
)2=（ ）
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分析：利用平方差公式，可将原式化为(a
+a-
+a
-a-
) •(a
+a-
-a
+a-
) ，进而根据am•a-m=1得到答案．
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解答：解：(a
+a-
)2-(a
-a-
)2
=(a
+a-
+a
-a-
) •(a
+a-
-a
+a-
)
=2a
•2a-
=4
故选B
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=(a
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=2a
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故选B
点评：本题考查的知识点是有理数指数幂的化简求值，熟练掌握平方差公式，及am•a-m=1是解答的关键．
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