Question

will give a medal: How do you know if a function varies directly?

Answer 1

http://www.sparknotes.com/math/algebra1/variation/section1.rhtml
http://www.millersville.edu/~bikenaga/basic-algebra/variation/variation.html
http://www.freemathhelp.com/direct-variation.html
http://www.freemathhelp.com/direct-variation.html

Answer 2

If the slope is constant, and 0,0 is possible solution.

Answer 3

Thank you :3