① y=lgcos(2x+π/4)的定义域② y=3sin(2x+π/4) x属于[0,π/2]..求最值和相应的x的值③ y=sin(-2x+π/4) 求单调递减区间
问题描述:
① y=lgcos(2x+π/4)的定义域
② y=3sin(2x+π/4) x属于[0,π/2]..求最值和相应的x的值
③ y=sin(-2x+π/4) 求单调递减区间
答
1.(2X+π/4)属于(-π/2+2kπ,π/2+2kπ);k属于Z
得:X属于(-3/8π+kπ,π/8+kπ),k属于Z
2.X=π/8时,有最大值3;X=π/2时,有最小值3/2倍根号2
3.(-2X+π/4)属于(π/2+2kπ,3π/2+2kπ);k属于Z
得:X属于(-5π/8+kπ,-π/8+kπ);k属于Z.注:k与-k等价,k属于Z时.