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Given that $x+y=10$ and $2x+y=13$, what is the value of $x^2-y^2$?

 Jul 15, 2015

Best Answer 

 #1
avatar+17747 
+10

  x + y  =  10     --->    -x - y  =  -10

2x + y  =  13     --->   2x + y  =  13

Add down the columns:  x  =  3

Substituting into the first equation:  y = 7

x2 - y2  =  (3)2 - (7)2 =  9 - 49  =  -40

 Jul 16, 2015
 #1
avatar+17747 
+10
Best Answer

  x + y  =  10     --->    -x - y  =  -10

2x + y  =  13     --->   2x + y  =  13

Add down the columns:  x  =  3

Substituting into the first equation:  y = 7

x2 - y2  =  (3)2 - (7)2 =  9 - 49  =  -40

geno3141 Jul 16, 2015

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