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2014-07-26T17:28:20+03:00
(2+5)²= 2² +5² +x

2² +2*2*5+ 5² =2² +5² +x

2*2*5=x

x=4*5

x=20
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2014-07-26T17:28:43+03:00
(2+5)² = 2²+5² +2·2·5
          = 4 + 25 + 20 

⇒x = 20 . 
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