How do I solve the linear systems by substitution?
y=x-3
y=-2x-6

Question

How do I solve the linear systems by substitution? 
y=x-3
y=-2x-6

solomonzelman · Answer

this is the system.
$\LARGE\color{blue}{ \sf     y=x-3 }$
$\LARGE\color{blue}{ \sf     y=-2x-6 }$

way 1
$\LARGE\color{blue}{ \sf     y=\color{red} {  x-3        }}$
substitute the red into the second equation
$\LARGE\color{blue}{ \sf    \color{red} {  x-3        }=-2x-6 }$

$\LARGE\color{blue}{ \sf    x-3        =-2x-6 }$  add 6 to both sides,
$\LARGE\color{blue}{ \sf    x+3        =-2x }$   subtract x from both sides,
$\LARGE\color{blue}{ \sf    3        =-3x }$  divide both sides by   -3  ,
$\LARGE\color{blue}{ \sf    ?        =x }$    can you tell me the result ?

solomonzelman · Answer

way 2 is just to substitute from second equation to the first

solomonzelman · Answer

or substitute y instead of x.