约分：x²-4/(x+7)(x-2);a的4次方-2a²+1/a²+2a+1.
问题描述：
约分：x²-4/(x+7)(x-2);a的4次方-2a²+1/a²+2a+1.
答
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