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Fie a,b,c,d (apartine) R , astfel incat a+b=20 si c+d= 30. calculati ac+ad+bc+bd

Răspuns :

ac+ad+bc+bd
a(c+d)+b(c+d)
30a+30b
30(a+b)
30*20
600
[tex]\displaystyle ac+ad+bc+bd= \\ \\ =a(c+d)+b(c+d)= \\ \\ =(a+b)(c+d)= \\ \\ =20 \cdot 30= \\ \\ =600.[/tex]