f(x)=1/(x²-2x+3)=1/(x²-2x+1+2)=1/[(x-1)²+2]
平方項(xiàng)恒非負(fù),(x-1)²≥0
(x-1)²+2≥2≠0,無(wú)論x取何實(shí)數(shù),函數(shù)表達(dá)式始終有意義,函數(shù)定義域?yàn)镽.
1/[(x-1)²+2]≤1/(0+2)=1/2
1>0 (x-1)²+2>0 f(x)>0
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