sinA+cosA=根号2（A+π/4）=tanAA属于 （0,π/2）则从（0,π/4）.函数单增,最小A趋向0时.sinA+cosA=1.而此时为0sinA+cosA>tanA当A增加时,sinA+cosA,tanA均是增函数,当A=π/4.则sinA+cosA=根号2.而tanA=1,则sinA+cosA...