已知x属于(-π/2,0),sinx+cosx=-根号2/31,求cos(x+π/4)的值2.求(cos2x)/[tanx+1/tanx]

问题描述:

已知x属于(-π/2,0),sinx+cosx=-根号2/31,求cos(x+π/4)的值2.求(cos2x)/[tanx+1/tanx]