Basic exercise with trinomial
Rearrange code to allow for fractions to be multiplied by constants
Add hints and answer for questions with additional coefficients
Improve hints
Add more exercise types
Fixes and accept even greater range of factored answers
Increase range of exercise type by multiplying some terms by the variable
Remove earlier exercise from another branch
Merge branch 'multi-rat4' of https://github.com/petercollingridge/khan-exercises

Conflicts:
	exercises/multiplying_and_dividing_rational_expressions_3.html
	utils/rational-expressions.js