You can use math.stackexchange.com for this today. It's frowned upon to just ask an exercise from a book w/o even trying to solve it, but if you show that you m

You can use math.stackexchange.com for this today. It's frowned upon to just ask an exercise from a book w/o even trying to solve it, but if you show that you made an effort but got stumped, or if you show your solution and ask if it's correct, people will gladly help you out.