iv used the following formula to work out an angle between 2 points in 3d space

cos t =((x1 * x2)+(y1*y2)+(z1*z2) )/ sqrt((x1*x1)+(y1*y1)+(z1*z1)) * sqrt((x2*x2)+(y2*y2)+(z2*z2))

which works fine, I now need to know if the angle returned is a positive angle or negative one