Question

x+3/3-x+x平方-9/x平方+6x+9 =[(x+3)²-(x-3)²]/(9-x²

Answer 1

(x+3)/(3-x)+(x-3)/(x+3)

=[(x+3)*(x+3)]/[(3-x)(x+3)]+[(x-3)(3-x)]/[(x+3)(3-x)]…………………………这一步是通分

=[(x+3)²-(x-3)²]/(9-x²)……………………………………分母相同,分子相加减

=[(x+3+x-3)(x+3-x+3)]/(9-x²)…………平方差公式a²-b²=(a+b)(a-b),这里a=x+3,b=x-3

=12x/(9-x²)………………算出结果

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