Question 587982
Find the exact value for each trigonometric function. 

cos 675 
675-360=315º=reference angle of 45º in quadrant IV where cos>0
cos 675º=cos 45º=√2/2

8. csc (-240) 
240-180=60º reference angle in quadrant II where csc <0
csc(-240)=csc 60º=-2/&#8730;3=-2&#8730;3/3

9. cot 900
900-720=180º
cot 900=cot 180=0 

10. tan 570 
570-360=210=reference angle of 30º in quadrant III where tan >0
tan 570=tan 30º=&#8730;3/3

11. sec (-780)
780-720=60º reference angle in quadrant IV where sec<0 
sec (-780)=sec 60º=-2

12. csc 90=1/sin 90º=1/1=1

Note: When given angle is negative rotate clockwise, when positive, rotate counter clockwise.