先化简,再求值:((3a)/(a-1)-(a)/(a+1))*(a²-1)/(a),其中a=8
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![先化简,再求值:((3a)/(a-1)-(a)/(a+1))*(a²-1)/(a),其中a=8](/uploads/image/z/635407-7-7.jpg?t=%E5%85%88%E5%8C%96%E7%AE%80%2C%E5%86%8D%E6%B1%82%E5%80%BC%EF%BC%9A%EF%BC%88%EF%BC%883a%EF%BC%89%2F%EF%BC%88a-1%EF%BC%89-%EF%BC%88a%EF%BC%89%2F%EF%BC%88a%2B1%EF%BC%89%EF%BC%89%2A%EF%BC%88a%26sup2-1%EF%BC%89%2F%EF%BC%88a%EF%BC%89%2C%E5%85%B6%E4%B8%ADa%3D8)
先化简,再求值:((3a)/(a-1)-(a)/(a+1))*(a²-1)/(a),其中a=8
先化简,再求值:((3a)/(a-1)-(a)/(a+1))*(a²-1)/(a),其中a=8
先化简,再求值:((3a)/(a-1)-(a)/(a+1))*(a²-1)/(a),其中a=8
原式=(3a)/(a-1)×(a²-1)/(a)-a/(a+1)×(a²-1)/(a)
=3(a+1)-(a-1)
=2a+4
将a=8代入得16+4=20
((3a)/(a-1)-(a)/(a+1))*(a²-1)/(a),
=(3a)/(a-1)-(a-1))
=(3a-(a²+1-2a))/(a-1)
=(-a²-1+5a)/(a-1)
=(-64-1+40)/7
=-25/7
答案是是18啊
原式为:(3a/a-1 -a/a+1)[(a²-1)/a]
=3a/a-1 ×a²-1/a -a/a+1 ×a²-1/a
=3a/a-1 ×(a+1)(a-1)/a -a/a+1 ×(a+1)(a-1)/a
=3(a+1)-(a-1)
=2a+4
再将a=8代人原式
原式=2a+4=2×8+4=20