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ab+ac+a=165
b+c=10
a=?


Răspuns :

ab+ac+a = a(b+c+1)
a(b+c+1) =165
a(10+1) = 165
11a = 165   |:11
a = 15
[tex]ab+ac+a=165 \\ b+c=10 \\ ab+ac+a=165 \\ a(b+c)+a=165 \\ 10a+a=165 \\ 11a=165 \\ a=165:11 \\ \boxed{a=15}[/tex]