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问题: 初二数学~~~分式方程~~~~~~~先化简再求值......

先化简再求值:
(a^2+3a)/(a^2+4a+4)÷(a+3)/(a+2)-2/(a+2),其中a=(√2)-2

解答:

(a^2+3a)/(a^2+4a+4)÷(a+3)/(a+2)-2/(a+2),其中a=(√2)-2
解:(a^2+3a)/(a^2+4a+4)÷(a+3)/(a+2)-2/(a+2)=
a(a+3)/(a+2)^2÷(a+3)/(a+2)-2/(a+2)=
[a(a+3)/(a+2)^2]×[(a+2)/(a+3)]-2/(a+2)=
a/(a+2)-2/(a+2)=
(a-2)/(a+2)=(其中a=(√2)-2)
(√2)-4)/√2=(2-4√2)/2=1-2√2