Question

Is substitutions the best method to use when one variable is already known

Answer 1

There’s two ways to substitute, but i think you mean if you know x but don’t know y. if that is true, then yes use substitution

Answer 2

Substitution Method is used for solving equations in 2 Variables, where you find the value of one variable in terms of the other and then substitute that value into any one of the equations. It can also be used when one Variable is known to you and you have to find the other.