Cos45*sin225+0.5ctg(-315)-cos270

сos45 °·sin225 °+0.5ctg(-315 °)-cos270 °=сos45°·sin(270°-45°)-0,5ctg315°-cos270°=cos45°·(-cos45°)-0,5ctg(360°-45°)=-cos²45°+0,5ctg45°+0= =-(√2/2)²+0,5·1=-2/4+0,5=-0,5+0,5=0