The words tri, try sound the same but have different meanings and spellings. Why do tri, try sound the same even though they are completely different words?
The answer is simple: tri, try are homophones of the English language.
triathlon
To make an effort to do or accomplish (something); attempt: tried to ski.
To taste, sample, or otherwise test in order to determine strength, effect, worth, or desirability: Try this casserole. Try the door.
Law To examine or hear (evidence or a case) by judicial process.
Law To put (an accused person) on trial.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").