Substitution Method of Algebra

Substitution:

In Algebra "Substitution" means putting numbers in correct places

Substitute:

"Substitute" means to put in the place of another.

If you have:  x-2

And you know that x = 6

Then you can "substitute" 6 for x:

6-2 = 4

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Sample problem for substitution method:

If x=2, then what is x + 10/x?

Substitute “2” in x + 10/x:

= 2 + 10/2

= 7

Examples:

Example problem in algebra: 1

If x=2 then what is 10/x + 4( use substitution method)?

Put "2" where "x" is:

=10/2 + 4

= 5 + 4

= 9
Example problem in algebra: 2

If x=2 and y=3, then what is x2 + xy?

Put "2" where "x" is and “3 where "y" is:

=22 + 2×3

= 4 + 6 = 10
Example problem in algebra: 3

If x=4 (but you don't know "y"), then what is x2 + xy?

Put "4" where "x" is:

= 42 + 4y

= 16 + 4y

Negative Numbers:

When substituting negative numbers, substitute () around them so you get the calculations right.
Example 1:

If x=-3, then what is 1-x+x2?

Put "(-3)" where "x" is:

= 1 - (-3) + (-3)2

= 1 + 3 + 9

= 13
Example 2:

If x=-3 and y=-4, then what is x2 + xy?

Put "-3" where "x" is and “-4 where "y" is:

= (-3)2 + (-3)(-4)

= 9 + 12

=21

Adding or Subtracting:

Two like signs become a positive sign:

3+ (+2) = 3 + 2 = 5

6-(-3) = 6 + 3 = 9

Two unlike signs become a negative sign:

7+ (-2) = 7 - 2 = 5

8-(+2) = 8 - 2 = 6

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Substitution Method problem:

To find x and y values: x + y = 20
y = x + 6
Solution:

lets Substitute the second equation solved for "y" into first equation in place of "y"

x + y = 20

x + x + 6 = 20

2x + 6 = 20

2x = 14

x = 7

Now use this to find the variable "y" by plugging this into second eq

y = x + 6

y = 7 + 6

y = 13

So, our answer is (7,13)

let’s check the answer

x + y = 20

7 + 13 = 20 True