Going through the proof for the quotient rule in Session 10, I can't figure out how the variable substitutions they use to prove the rule [substituting delta u and delta v for u(X+deltaX)-u(X) and v(X+deltaX)-v(X)] help the simplification. I can't even figure out where they get the above long expressions to simplify into the substitute variables! Any help would be appreciated!

Question

phi · Answer

Does this help?

anonymous · Answer

Thanks, that did help! Appreciate it!