约分：x²-4/(x+7)(x-2);a的4次方-2a²+1/a²+2a+1.
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约分：x²-4/(x+7)(x-2);a的4次方-2a²+1/a²+2a+1.约分：x²-4/(x+7)(x-2);a的4次方-2a²+1/a
约分：x²-4/(x+7)(x-2);a的4次方-2a²+1/a²+2a+1.
约分：x²-4/(x+7)(x-2);a的4次方-2a²+1/a²+2a+1.
约分：x²-4/(x+7)(x-2);a的4次方-2a²+1/a²+2a+1.
x²-4/(x+7)(x-2)
=(x+2)(x-2)/(x+7)(x-2)
=(x+2)/(x+7)
a的4次方-2a²+1/a²+2a+1.
=(a²-1)²/(a+1)²
=(a+1)²(a-1)²/(a+1)²
=(a-1)²