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25 July, 00:14

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

+3
Answers (1)
  1. 25 July, 00:40
    0
    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
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