More info here , notes here, and on pages 362-364 in book

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Steps for substitution:

1) **Isolate** a variable (for instance x=... or y=...)

2) **Substitute** the isolated variable in for itself in the other equation.

3) **Solve** the new equation which now has only one variable

4) Use the value of the variable to **plug in** to one of the original equations to find the missing side of the coordinate pair.

Example:

For the equations, y+2=2x and 2y+3x=10

What are the coordinates of the simultaneous solution?

ISOLATE: Easiest to isolate y in first equation by adding 2 to both sides: y=2x-2

SUBSTITUTE: 2(2x-2)+3x=10

SOLVE: 4x - 4 + 3x = 10 ==> eventually gets you 7x = 14 which means x=2

PLUG IN: Pick either of the two equations to plug in x=2. You should get the same answer for y.

y + 2 = 2(2)

gives

y = 2

whereas

2y+3(2)=10

also gives

y=2

So the solution is (2,2)