Please see my answer above for a definition of reference angle.
Because 141° has a reference angle of 39°, it will have the same trig values as 39°. We recall that the sine value of an angle is the y-coordinate of the point of intersection between the angle and the unit circle. The cosine value is the x-coordinate of that point. So sin39° = .629 and cos39° = .777 and we can conclude, using reference angle logic and ASTC, that sin141° = .629 and cos141° = - .777.
By similar logic, sin289° = - .946 and cos289° = .326.
It will be instructive for you to sketch these angles in the coordinate plane in standard position along with the unit circle to see why the above answers are true.
