cos225°+tan960°+sin(-1140°)+cot(-570°)
=cos(180°+45°)+tan(720°+240°)+sin(-1080°-60°)+cot(-360°-210°)
=-cos45°+tan(180°+60°)-sin60°+cot(-180°-30°)
=-cos45°+tan60°-sin60°-cot30°
=-√2/2+√3-√3/2-√3
=-(√3+√2)/2