怎么证明（2-x)(x-3)(x的平方-5x-14)小于等于100

证明：
（2-x)(x-3)(x的平方-5x-14)-100
=-(x-2)(x-3)(x²-5x-14)-100
=-(x²-5x+6)(x²-5x-14)-100
=-(x²-5x)²+8(x²-5x)+84-100
=-(x²-5x)²+8(x²-5x)-16
=-[(x²-5x)²-8(x²-5x)+16]
=-(x²-5x-4)²
≤0
所以（2-x)(x-3)(x的平方-5x-14)≤100