Question

Fie a, b, c, d aparine R, astfel incat a+b=20 si c+d=30. Calculating ac+ad+bc+be.

Answer 1

ac+ad+bc+bd = a(c+d)+b(c+d) ; inlocuim c+d=30 ⇒ 30a+30b = 30(a+b)=

=30x20 = 600 ; stiind ca a+b =20

Answer 2

ac + ad + bc + bd = 600

= a × ( c + d ) + b × ( c + d ) =

= ( c + d ) × ( a + b ) =

= 30 × 20 =

= 600