Resol el sistema: x + y = 4, 2x-y = 5?

Resposta:

y = 1

x = 3

Explicació:

# x + y = 4 # --- (1)

# 2x-y = 5 # --- (2)

De (1),

# x + y = 4 #

# x = 4-y # --- (3)

Sub (3) a (2)

# 2x-y = 5 #

# 2 (4-y) -y = 5 #

# 8-2y-y = 5 #

# 8-3 = 5 #

# 3 = 3y #

# y = 1 # --- (4)

Sub (4) a (3)

# x = 4-y #

# x = 4-1 #

# x = 3 #