题目

很急很急,在线等 f(x)=2sin(π/2-x/2)*sin(π+x/2)+cos平方(π/2-x/2)-cos平方(π+x/2)
f(x)=2sin(π/2-x/2)*sin(π+x/2)+cos平方(π/2-x/2)-cos平方(π+x/2) (1)若x属于（0,π/2）求f(x)最小值（2）设g(x)=f(2x-π/4）+2m,x属于｛π/4,7π/8｝,若g(x)有两个零点,求m的范围

提问时间：2020-10-30

答案

f(x)=2sin(π/2-x/2)*sin(π+x/2)+cos²(π/2-x/2)-cos²(π+x/2)=-2cos(x/2)sin(x/2)+sin²(x/2)-cos²(x/2)=-sinx-cosx=-√2sin(x+π/4)
∵x∈(0,π/2)
∴x+π/4∈(π/4,3π/4)
∴当x=π/4时f(x)取得最小值-√2
g(x)=f(2x-π/4)=-√2sin(2x+π/4)+2m
∵x∈(π/4,7π/8)
∴2x+π/4∈(3π/4,2π)
∴-√2sin(2x+π/4)∈(-1,√2]
∴0<-2m<√2
∴m的范围为-√2/2太复杂了!请楼主加分!