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