What are the steps of the addition and substitution methods?
Can someone break down the steps of how to identify whether an equation needs addition or substitution or both? Thanks.
Most always, you can do either one. Substitution is often easier when one variable is all by itself, or easy to get all by itself, as in"
2x + 3y = 8
x = y - 1
You’d just substitute (y - 1) for the x in equation 1 getting 2(y - 1) + 3y = 9
2y - 2 + 3y = 8
5y - 2 = 8
5y = 10
y = 2 then plug that in to get x.
But if it’s not easy to get a variable by itself, addition is usually easier. As in
2x + 3y = 8
4x + 7y = 18
You would multiply row 1 by -2 then add it to row 2 which will eliminate the x:
-4x -6y = -16
4x + 7y = 18
—————
1y = 2
so again y = 2; plug in to get x
That’s basically it
February 10th, 2010 at 11:25 am
it really just depends on what they ask for, and what is easiest. If they don’t specify one or the other, just do it one way, and if that’s too hard, try it the other way
References :
February 10th, 2010 at 12:09 pm
Usually when you have a large equation, you are to use "PEMDAS" which stands for Parenthesis-Exponents-Multiply-Divide-Add-Subtract. This is the order in which the problem should be solved, starting with numbers in parenthesis, then numbers with exponents and so on.
Hope this is what you were asking for. ; )
References :
Math Class.
February 10th, 2010 at 12:48 pm
Most always, you can do either one. Substitution is often easier when one variable is all by itself, or easy to get all by itself, as in"
2x + 3y = 8
x = y - 1
You’d just substitute (y - 1) for the x in equation 1 getting 2(y - 1) + 3y = 9
2y - 2 + 3y = 8
5y - 2 = 8
5y = 10
y = 2 then plug that in to get x.
But if it’s not easy to get a variable by itself, addition is usually easier. As in
2x + 3y = 8
4x + 7y = 18
You would multiply row 1 by -2 then add it to row 2 which will eliminate the x:
-4x -6y = -16
4x + 7y = 18
—————
1y = 2
so again y = 2; plug in to get x
That’s basically it
References :