Amethod of solving a system of equations in which one variable is replaced by an expression using the other variable as a representation for that variable.

i need to know what this is called

Substitution method.

Step-by-step explanation:

Using the substitution method is very easy, you have a system of equations like the next one:

x+y=7

x-y=3

So you clear one of them for one of the variable and then substitute that cleared variable in the other equation:

x=3+y

*x+y=7

*(3+y)+y=7

*3+2y=7

*2y=7-3

*2y=4

*y=2

That is hte method of substitution.

the first one, all those points on the line just make a strait line.