I don't understand the substitution method?

How do you solve problems like

6x+2y=-10

2x+2y=-10

Or

a+b=1

5a+3b=-1

It depends on what variable you are tying to solve for first. Say you are trying to solve for x first and then y on the first problem you wrote.

In substitution you solve one of the equations for example with

6x+2y=-10

2x+2y=-10

you solve 2x+2y=-10 for x

2x+2y=-10

-2y = - 2y (what you do to one side of the = you do to the other)

2x=-10-2y (to get the variable by its self you divide the # and the variable)

/2=/2 (-10/2=-5 and - 2y/2 = - y or - 1y, they are the same either way)

x=-5-y

now you put that in your original equation that you didn't solve for:

6 (-5-y) + 2y=-10 solve for that

-30-6y+2y=-10 combine like terms

-30-4y=-10 get the y alone and to do this you first get the - 30 away from it

+30=+30

-4y=20 divide the - 4 from each side

/-4=/-4 (20/-4=-5)

y=-5

now the equation you previously solved for x can be solved for y.

x=-5-y

x=-5 - (-5) a minus parenthesis negative - ( - gives you a positive

-5+5=0

x=0

and now we have solved the problem. x=0 and y=-5