设f(x一1)= x2+1,a>0,f(a)=17,则a=______.

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问题 设f(x一1)= x2+1,a>0,f(a)=17,则a=______.

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答案3

解析 因为f(x一1)=x2+1=(x一1)2+2x=(x一1)2+2(x一1)+2,
所以f(x)=x2+2x+2,
f(a)=a2+2a+2=17,则a=3.
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