先化简,再求值:(1)(2a/a²-4)+(1/2-a),其中a=1/2
(2)(a+2b/a+b)+(2b²/a²-b²)-(2ab/a²-b²),其中a=-2,b=1/3...
(2)(a+2b/a+b)+(2b²/a²-b²)-(2ab/a²-b²),其中a=-2,b=1/3
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(2a/a²-4)+(1/2-a)
=2a/(a+2)(a-2)-(a+2)/(a+2)(a-2)
=[2a-(a+2)]/(a+2)(a-2)
=(2a-a-2)/(a+2)(a-2)
=(a-2)/(a+2)(a-2)
=1/(a+2)
把a=1/2代入原式
原式=1/(1/2+2)=1/(5/2)=2/5
(a+2b/a+b)+(2b²/a²-b²)-(2ab/a²-b²)
=(a+2b)/(a+b)+(2b²-2ab)/(a+b)(a-b)
=(a+2b)/(a+b)+[2b(b-a)]/(a+b)(a-b)
=(a+2b)/(a+b)-2b/(a+b)
=(a+2b-2b)/(a+b)
=a/(a+b)
把a=-2,b=1/3代入原式
原式=-2/(-2+1/3)
=-2/(-5/3)
=6/5
=2a/(a+2)(a-2)-(a+2)/(a+2)(a-2)
=[2a-(a+2)]/(a+2)(a-2)
=(2a-a-2)/(a+2)(a-2)
=(a-2)/(a+2)(a-2)
=1/(a+2)
把a=1/2代入原式
原式=1/(1/2+2)=1/(5/2)=2/5
(a+2b/a+b)+(2b²/a²-b²)-(2ab/a²-b²)
=(a+2b)/(a+b)+(2b²-2ab)/(a+b)(a-b)
=(a+2b)/(a+b)+[2b(b-a)]/(a+b)(a-b)
=(a+2b)/(a+b)-2b/(a+b)
=(a+2b-2b)/(a+b)
=a/(a+b)
把a=-2,b=1/3代入原式
原式=-2/(-2+1/3)
=-2/(-5/3)
=6/5
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