Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

This question was from my class test. I would like to know how to solve it.

Thank you for your help.

enter image description here

share|cite|improve this question
1  
How about you start and we'll chime in? – rschwieb Jul 25 '12 at 23:28

Try $\varphi=u^-$; if you are unfamiliar with this notation, it means $\max(-u,0)$.

share|cite|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.