I need your help in Math?

Question

How do I know if an eqaution is a fucntion?

example:

1.) y = the sqareroot of (x - 9)

2.) y = 3x + 7

pls show me how do you do it


Thanks!

Answer 1

1.is not function as for each value of x there will be two values of y

2.y=3x+7 is a function as for each value of x there will be a unique value of y

Answer 2

A function can only have one answer for each number you plug in. If you ever could possibly get two answers, it's not a function.

The most common example is roots that can have positive or negative answers. (Depending on how your book does things, #1 above might or might not be considered a function. Most likely it is, because without a +/- sign, it's usually just the positive root that is indicated.

Other examples are trig problems that can have multiple solutions and problems that say > or < instead of =.

A "normal" equation like the line in #2 always has just one answer and is always a function.