证明：
(x²-4﹚﹙x²-10x+21﹚+100
=(x+2)(x-2)(x-3)(x-7)+100
=(x²-5x-14)(x²-5x+6)+100
=(x²-5x)²+6(x²-5x)-14(x²-5x)-84+100
=(x²-5x)²-8(x²-5x)+16
=(x²-5x-4)²
因为(x²-5x-4)²是一非负数,所以多项式(x2-4﹚﹙x2-10x+21﹚+100的值一定是非负数.