A certain manufacturer uses the function C(x)=0.04x2-8.5x+25,000 to calculate the cost, in dollars, of producing x thousand units of its product. The table above gives values of this cost function for values of x between 0 and 50 in increments of 10. For which of the following intervals is the average rate of decrease in cost less than the average rate of decrease in cost for each of the other intervals?
From x=0 to x=10
From x=10 to x=20
From x=20 to x=30
From x=30 to x=40
From x=40 to x=50
in increments of 10=选项中给的范围是按照10来递增的!!不跟倍数有关
【引用】
正确答案为E. 试着画一个向上抛物线,越靠近中心,减少的速率越慢。40-50区间是最靠近中心轴的
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