Question

How do you solve by substitution `y – 3x = 7` and `21 + 9x = 3y`?

Answer 1

`(x, y) = (x, 7 +3x)`

Explanation:

Equation 1: `y - 3x = 7=> y = 7 + 3x`

Substitution : Substitute 7 + 3x for y in the equation 2:

`21 + 9x = 3y`
`21 + 9x = 3(7 + 3x)`
`21 + 9x = 21 + 9x`
It is true for all real numbers => x can be any real number

`y = 7 + 3x`

Equation 1 and 2 are the same line, and the answers is `(x, 7 + 3x)`.