For my Japanese class we recently went over how to say stuff about playing instruments, but looking online had me confused about how to use a certain couple of verbs. I know that my textbook says ヴァイオリンをひく（弾く）, but online I've also encountered this other reading of the same kanji and I'm not sure the difference between ヴァイオリンをはじく（弾く）. Can anybody explain the difference please?
For this analysis, let's ignore the kanji.
The verbs we're dealing with are hiku and hajiku.
Underlying meaning of "to pull, to draw".
In the context of stringed instruments, this verb refers to the act of pulling or drawing a bow across the strings to produce a sound. By extension, this also came to refer to the act of producing sound from the strings of a piano or other keyboard instrument.
Underlying meaning of "to cause something to bend and pop back into place with force: to flick, to pluck, to let loose (as a bowstring)".
In the context of stringed instruments, this refers to the act of plucking the strings to produce sound.
Given the meanings of the verbs, one can both hiku a violin, and hajiku a violin. (Though probably not at the same time. :) )
According to the dictionary, 弾く is usually read as はじく.
But when it means to "to play a musical instrument", it must be read as ひく: