1) w=(x-20)y=(x-20)(-10x+500)=-10(x-20)(x-50)=-10[x^2-70x+1000]=-10[(x-35)^2-225]=-10(x-35)^2+2250
当x=35时,利润w最大,为2250元.
2）由w=-10(x-35)^2+2250=2000
得：(x-35)^2=25
x-35=5或-5
即x=40或30元.
1) w=(x-20)y=(x-20)(-10x+500)=-10(x-20)(x-50)=-10[x^2-70x+1000]=-10[(x-35)^2-225]=-10(x-35)^2+2250
当x=35时,利润w最大,为2250元.
2）由w=-10(x-35)^2+2250=2000
得：(x-35)^2=25
x-35=5或-5
即x=40或30元.