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Algebra - Substitution

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

Substitution

In Algebra "Substitution" means putting numbers where the letters are:

If you have:
x - 2
And you know that x=6 ...  
... then you can "substitute" 6 for x:
6 - 2 = 4

 

Example 1: If x=5 and y=3, then what is 10/x + 2y ?

Put "5" where "x" is, and "3" where "y" is: 10/5 + 2×3 = 2 + 6 = 8

 

Example 2: If x=3 and y=4, then what is x2 + xy ?

Put "3" where "x" is, and "4" where "y" is: 32 + 3×4 = 9 + 12 = 21

 

Example 3: If x=3 (but you don't know "y"), then what is x2 + xy ?

Put "3" where "x" is: 32 + 3y = 9 + 3y (that is as far as you can get)

 

As that last example showed, you may not always get a number for an answer, sometimes just a simpler formula.