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.
\[a=b^2++2cd=b^2++2(b+d)d=b^2+2bd+2d^2\]

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