Algebra definitions: need to find the words the def's define

I've been working on a vocabulary crossword in my summer math packet :shock: but I can't seem to find or think of the words for two definitions. If it's possible could someone tell me what these words are?

The two definitions are as follows :arrow:

1) "A relationship between the input and output"

2) "A number when substituted in an open sentence makes a true statement."

Please help if you can, thanks a million bye

Since this is a crossword, can you not give us the length of the 2 answers,
like how many letters in each?