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a+b=20   c+d=30
ac+ad+bc+bd=?


Răspuns :

ac+ad+bc+bd=a(c+d) +b(c+d)=(c+d)(a+b)=20 ori 30=600
30 ori 600=18000
ac+ad+bc+bd=a(c+d)+b(c+d)=(a+b)(c+ d)=20x30=600