## Substitution

There are two types of substitution.
1. Given an equation and some values of different quantities, we can substitute the values of those quantities into the equation.
Example:
$v=3z^2-2(x+y)$
. If
$x=4, \: y=1, \: z=2$
then
$v=3z^2-2(x+y)=3 \times 2^2-2(4+1)=2$

3. We can substitute equations into other equations. Let
$a=b^2++2cd$
and
$c=b+d$
then we can substitute the second of these into the first.
$a=b^2++2cd=b^2++2(b+d)d=b^2+2bd+2d^2$