✔ 最佳答案
1. f(x)=(x-20)(3000-100x)= -100x^2+5000x-60000
2. let y= -100x^2+5000x-60000
=-100(x^2-50x+600)
=-100(x^2-50x+25^2-25^2+600)
=-100[(x-25)^2-625+600)
=-100[(x-25)^2-25]
=-100(x-25)^2+2500
the max value of y is 2500.
when y=2500, x=25.
每隻玩具以$25出售才得最大盈利
3.
g(2x)=-100(x-25)^2+2500
=-100x^2+5000x-60000
=-25(2x)^2+2500(2x)-60000
=-25[(2x)^2-100(2x)+2400]
=-25[(2x)^2-100(2x)+50^2-50^2+2400]
=-25[(2x-50)^2-2500+2400]
=-25(2x-50)^2+2500
g(x)=-25(x-50)^2+2500
4.
g(x)=-25(x-50)^2+2500=2100
-25(x-50)^2=-400
(x-50)^2=16
x-50=+4 or -4
x=54 or 46
那盒拼圖以$54 or $46出售才得$2100的盈利