（1）sin765（2）cos(-1020）（3）tan(97π/6）（4）cot(-39π/6）（5）sin(-120

sin764=sin(360*2+45)=sin45=√2/2
cos(-1020)=cos(360*3-1020)=cos60=1/2
tan(97π/6=tan(96π/6+π/6)=tan(π/6)=√3/3
cot(-39π/6）=cot(42π/6-39π/6）=cot(2/π)=0
sin(-120)tan(-120)+cos(-135)cot(420)+sin(3π/2）=
-sin(-120+180)tan(180-120)-cos(180-135)cot(420-360)-1
=-sin60tan60-cos45tan60-1
=-3/2-√6/2

（1）sin765＝sin(720+45)=sin45=√2/2
（2）cos(-1020）=cos(-1080+60)=cos60`=1/2
（3）tan(97π/6）=tan(96π/6+π/6)=tan(π/6)=√3/3
（4）cot(-39π/6）=cot(-48π/6+9π/6)=cot3π/2=0
（5）sin(-120)tan(-120)+cos(-...

sin765=sin(720+45)=sin45=√2/2
cos(-1020）=cos1020=cos(3*360+40)=cos40
tan(97π/6）=tan(16π+π/6)=tanπ/6=√3/3
cot(-39π/6）=-cot(39π/6)=-cot(6π+π/2)=-cot(π/2)=0
sin(-120)tan(-120)+cos(-135)cot(420)+sin(3π/2）
=(-sin60)tan60+(-cos45)cot60-1
=-√3/2*√3-√2/2*√3/3-1
=-3/2-√6/2