Question

Ajutati-ma va roog!
Daca x +2y=9 si 3x +5y =23 , calculati 4x+7y

Answer 1

x+2y = 9
3x + 5y = 23
 x+ 2y +3x + 5y = 9 + 23
4x +  7y = 32

Answer 2

x + 2y = 9 => x = 9-2y
3x + 5y =23

inlocuim in ecuatia initiala: (pe x cu "9-2y")

3 (9-2y) + 5y = 23
27 - 6y + 5y = 23
27 -y = 23
-y = 23 -27 => -y = -4 => y =4

x + 2y = 9
x + 2 ×4 = 9
x + 8 = 9 => x =1

4x + 7y = 4 ×1 + 7×4 = 4 + 28 => 32
4x + 7y = 32