Moreover, because the unit price of this commodity is reduced by 1 yuan, 20 more pieces will be sold every day, so when the unit price is reduced by (40-x) yuan, 20(40-x) pieces can be sold, and the number of pieces sold every day is [200+20(40-x)].
(2)y=(x-20)[200+20(40-x)]=(x-20)( 1000-20x)=-20(x^2-70x+ 1000)
Turn the general formula of quadratic function into a vertex: y =-20 (x2-70x+1000) =-20 (x-35) 2+4500.
The parabola opens downward, and the maximum value is obtained at the vertex.
Therefore, when the unit price is 35 yuan, the goods get the maximum profit, and the maximum profit is 4500 yuan.