y=(35-x)(50+2x)
=1750+70x-50x-2x²
=-2x²+20x+1750
=-2(x²-10x)+1750
=-2(x²-10x+25-25)+1750
=-2(x-5)²+1800
所以当每件商品降价5元时,可使每天的销售额最大,最大销售额是1800元
y=(35-x)(50+2x)
=1750+70x-50x-2x²
=-2x²+20x+1750
=-2(x²-10x)+1750
=-2(x²-10x+25-25)+1750
=-2(x-5)²+1800
所以当每件商品降价5元时,可使每天的销售额最大,最大销售额是1800元