åå¼=ï¼X-3)(X+3)²-(X+3)(X+5)(X-3)
=(X-3)(X+3)(X+3)-(X+3)(X+5)(X-3)
=ï¼X-3)(X+3)(x+3-x-5ï¼
=-2(X-3)(X+3)
å 为 X=-3
æ以 该å¼=0
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