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问题: 初3数学...

一家店卖面粉,1袋进价40元,当售价定为50元时可卖出500袋,每涨1元就少卖10袋,设销售价为X,利润为Y,1,问Y与X的函数解析式? 2售价定为多少时,能获得最大利润....

解答:

Y=(X-40)(500-10*(X-50)) X>=50

Y=(X-40)(500-10*(X-50))
=(X-40)(500-10X+500)
=-10(X-40)(X-100)
=-10(X^2-140X+4000)
=-10(X^2-2*70X+4900-900)
=-10((X-70)^2-900)
=-10(X-70)^2+9000
X=70,Y=9000最大值