Question

What's the difference between j(x) and just X in j(x)=-2x+4 ??

Answer 1

J(x) is equivalent to Y. For example if you were to have a equation in slope intercept form it would be y=mx+b which can be written in the same way as your problem j(x)=mx+b. To sum it up j(x) is just another way to say y=