Question

va rog dau coroana

Calculati

a) Dacă a + b = 20 și b + c = 30, calculați 3 ⋅ a + 7 ⋅ b + 4 ⋅ c.
b) Dacă a + b = 33 și a + c = 11, calculați 5 ⋅ a + 3 ⋅ b + 2 ⋅ c.

Answer 1

a)   a + b = 20   si b + c = 30

3 × a + 7 × b + 4 × c = 180

= 3 × a + 3 × b + 4 × b + 4 × c =

= 3 × ( a + b ) + 4 × ( b + c ) =

= 3 × 20 + 4 × 30 =

= 60 + 120 =

= 180

______________________

b)     a + b = 33  si   a + c = 11

5 × a + 3 × b + 2 × c = →   5 × a = 3 × a + 2 × a ⇒ suma de 2 produse

= 3 × a + 3 × b + 2 × a + 2 × c =

= 3 × ( a + b ) + 2 × ( a + c ) =

= 3 × 33 + 2 × 11 =

= 99 + 22 =

= 121