Question

How do you solve `x + y = 4` and `9x + 9y = 36`?

Answer 1

`y = 4-x` for any `x in RR`

Explanation:

These two equations both describe the same line. Any point on the line is a solution, so there are an infinite number of solutions.

For example, given any `x in RR`, let `y = 4-x`.

graph{x+y=4 [-10, 10, -1.72, 8.28]}