# Substitution method

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• Nov 4th 2007, 10:41 PM
Mr Rayon
Substitution method
Find the points of intersection between the following equations for straight lines using the substitution method.

y=x+5 and 5x-y=-1

&

y=x-3 and 2x-y=7
thx
• Nov 4th 2007, 11:16 PM
angel.white
Quote:

Originally Posted by Mr Rayon
Find the points of intersection between the following equations for straight lines using the substitution method.

y=x+5 and 5x-y=-1

&

y=x-3 and 2x-y=7
thx

EQ1:
You know that y=x+5, so substitute "x+5" in for y in the other equation

5x-y=-1
5x-(x+5)=-1
5x-x-5=-1
4x-5=-1
4x=4
x=1

Now just substitute "1" in for x in either equation

5x-y=-1
5(1)-y=-1
5-y=-1
-y=-6
y=6

Now you try for the second equation.
• Nov 5th 2007, 05:21 AM
Mr Rayon
Is this right?

y=x-3
2x-y=7
2x-(x-3)=7
2x-x+3=7
x+3=7
-3 -3
x=4
y=4-3
y=1

So x=4 and y=1 (4,1)
• Nov 5th 2007, 09:16 AM
topsquark
Quote:

Originally Posted by Mr Rayon
Is this right?

y=x-3
2x-y=7
2x-(x-3)=7
2x-x+3=7
x+3=7
-3 -3
x=4
y=4-3
y=1

So x=4 and y=1 (4,1)

Yep, you got it! :)

-Dan
• Nov 6th 2007, 09:31 AM
dravid2
oh i understand now