证明如下：
A=(x+2)(x-3)(x+4)(x-5)+49
=(x²-x-6)(x²-x-20)+49
=x^4-2*x^3-25x²+26x+169
=(x²)²-2*x²*x+x²-26x²+26x+169
=(x²-x)²-2*13*(x²-x)+13²
=[(x²-x)²-13]² 亲!记得给采纳哦!演讲之家小编!