1. Math is complex but useful.
2. Math is complicated but useful.
(Are both okay? Which syllable is stressed in 'complex'? First syllable or second syllable? There seem to be two ways in the dictionary.)
COMplex is a noun
comPLEX is an adjective
Similar to
PROtest: noun
proTEST: verb
(though you'd never guess it if you listen to the news...)
In your sentence 1, you'd use the second pronunciation Steve gave you for "complex."
Both are fine to use as adjectives in your sentences, yes.
Both sentences are correct and convey the same meaning. The word "complex" can be pronounced with the stress on either the first syllable or the second syllable, depending on regional variations or personal preference.
To determine the correct stress in a word, you can consult a dictionary. Dictionaries usually provide pronunciation guides that indicate where the stress falls in a word. For example, a dictionary may use symbols like a straight line ( ˈ ) before the stressed syllable.
If you have access to an online dictionary or a dictionary app, you can search for the specific word and it should provide you with the correct pronunciation and stress pattern. Additionally, many online dictionaries also provide an audio pronunciation feature, which can be helpful in understanding the correct stress pattern.