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daca x patrat - y patrat = 63 si x-y = 7 atunci x+y = ?

Răspuns :

x²-y²=63, x-y=7,

x²-y²=(x+y)(x-y)=63, 7(x+y)=63, ⇒x+y=63/7=9

x² - y² = 63

x² - y² = ( x - y ) ( x + y )

( x - y ) ( x + y ) = 63

7 ( x + y ) = 63

x + y = 63 : 7

x + y = 9