what is substitution

Question

algebra problems with answers

Answer 1

Substitution is the process of replacing a variable with a know value (either a constant or an expression of variables).

For example, I could give you an equation that says a + b = c.  I could also tell you that a = 2 and b = 4.  I would then show the following work to find c:

a + b = c               Given

2 + 4 = c               Substitution

6 = c

 

Substitution can also involve expressions.  If an expression is solved for a variable, then the entire expression can take the place of the same variable in other equations for the same problem.

For example, I have two equations x + y = 4 and 2x - y = 2.  I can solve one of the equations for a variable and then substitute it into the other equation:

x + y = 4              Given (equation 1)

x + y - x = 4 -x     Subtract x from each side

y = 4 -x               Simplify

2x - y = 2            Given (equation 2)

2x - (4 -x) = 2     Substitution