+0  
 
0
97
1
avatar+169 

25^x - 9^x = 18

 

5^x  - 3^x = 3

 

What's 5^x + 3^x = ?

 Jun 30, 2018
 #1
avatar+94545 
+1

Not as hard as it looks....!!!!

 

Note that  25^x  - 9^x   can be written as   (5^x)^2  - (3^x)^2

 

And this will factor as a difference of squares as

 

( 5^x - 3^x)  (5^x  + 3^x)  

 

And since this equals 18  and (5^x - 3^x)  = 3

 

Then  (5^x + 3^x)   must  = 6

 

 

cool cool cool

 Jun 30, 2018

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