I think one answer for -5pi/ 3 would be pi/3 ???
-5pi/3 = - 300° = 360 - 300 = 60° = pi/3 (good job!!!)
8pi/7 = a litle more difficult....8pi/7 = pi + pi/7
Compare to 22pi/7 = 14pi/7 + 8pi/7 = 2pi + 8pi/7
So 8pi/7 = 22pi/7