✔ 最佳答案
f(x)=2sin^2x-2sinx+3=2(sinx-(1/2))^2+(5/2)
因-1<=sinx<=1
==>(-1)-(1/2)<=(sinx-(1/2))<=1-(1/2)
==>-3/2<=(sinx-(1/2))<=1/2
==>1/4<=(sinx-(1/2))^2<=9/4
==>1/2<=2(sinx-(1/2))^2<=9/2
==>(1/2)+(5/2)<=2(sinx-(1/2))^2+(5/2)<=(9/2)+(5/2)
==>3<=2(sinx-(1/2))^2+(5/2)<=7
其極大值為7
其極小值為3
2015-02-14 17:26:23 補充:
更正第五行以後
==>0<=(sinx-(1/2))^2<=9/4
==>0<=2(sinx-(1/2))^2<=9/2
==>0+(5/2)<=2(sinx-(1/2))^2+(5/2)<=(9/2)+(5/2)
==>5/2<=2(sinx-(1/2))^2+(5/2)<=7
其極大值為7
其極小值為5/2
2015-02-15 00:18:17 補充:
簡化算式
當配成配方後可視為拋物線,因領導係數為正,表有最低點.
因正弦值域在正負1之間,將值代入,可求極大值.