Question

1.求值:sin 390-cos 120-tan 225+cos(－45°)

Answer 1

解:原式=sin(360十30)-(-1/2)-1十√2/2二1/2十1/2-1十√2/2=√2/2

Answer 2

sin390=sin(360+30)=sin30=1/2
cos120=cos(180-60)=-cos60=-1/2
tan225=tan(180+45)=tan45=1
cos(－45)=cos45=√2/2
∴=√2/2