SOLUTION: 3X-9Y=18 AND 4X+3Y=12 HOW DO I SOLVE AND GRAPH THIS LINEAR EQUATION

Algebra ->  Linear-equations -> SOLUTION: 3X-9Y=18 AND 4X+3Y=12 HOW DO I SOLVE AND GRAPH THIS LINEAR EQUATION      Log On


   

Question 1024555: 3X-9Y=18 AND 4X+3Y=12
HOW DO I SOLVE AND GRAPH THIS LINEAR EQUATION
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
You have 2 equations and 2 unknowns.
As long as the number of equation is
the same or more than the number of
unknowns, you can solve.
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(1) +3x+-+9y+=+18+
(2) +4x+%2B+3y+=+12+
--------------------
Multiply both sides of (2) by +3+
and add (1) and (2)
(1) +3x+-+9y+=+18+
(2) +12x+%2B+9y+=+36+
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+15x+=+54+
+x+=+54%2F15+
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+x+=+18%2F5+
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(1) +3x+-+9y+=+18+
Divide both sides by +3+
(1) +x+-+3y+=+6+
Plug in solution +x+=+18%2F5+
(1) +18%2F5+-+3y+=+6+
Multiply both sides by +5+
(1) +18+-+15y+=+30+
(1) +15y+=+-12+
(1) +y+=+-4%2F5+
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The solution ( point where lines intersect ) is:
( 18/5 , -4/5 )
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Here's the plot: