determinedI was determined not to give up.
persistentThe shop never gives refunds, but if you are persistent, they may.
resolvedformalI am resolved to do something about the issue.
resoluteformalWe must remain resolute in the face of opposition.
single-mindedShe was single-minded and uncompromising in her work.
tenaciousHe is tenacious in fighting for causes he believes in.
pertinaciousformalThe couple’s pertinacious demands to have the law changed for their benefit were a constant source of aggravation for the council.
perseveringShe was described as a persevering woman with great willpower.
perseverantformal,old-fashionedScientists are very perseverant people.