Y=1-3COS(3X-π/4)。求函数最值。并求出相应的集合

cos=1，y最小=1-3=-2
此时3x-π/4=2kπ
3x=2kπ+π/4
所以x=2kπ/3+π/12
cos=-1，y最大=1+3=4
此时3x-π/4=2kπ+π
3x=2kπ+5π/4
所以x=2kπ/3+5π/12

综上
x=2kπ/3+5π/12，y最大=4
x=2kπ/3+π/12，y最小=-2

Y=1-3COS(3X-π/4)
Domain: 0<x<2pi => -pi/12 <3(x-pi/4) < 3(2pi - pi/12)
let 3x-pi/4 = m
y=1-3cos(m)
3cos(m)=1
cos(m)=1/3
basic angle= cos^-1 (1/3) = 1.23096rad
.: cos +ve in first and fourth quad
m = 1.23096, 2pi - 1.23096, 2pi + 1.23096, 4pi - 1.23096, 4pi + 1.23096
m = 3x-pi/4
x= [1.23096+(pi/4)]/3....... sub in the rest yourself :D