Com es resol el sistema següent: 7x + y = -2, -7x + y = -9

# 7x + y = -2 ……………….. (i) #

# -7x + y = -9 …………………… (ii) #

Afegiu (i) i (ii)

#implies 2y = -11 #

#implies y = -11 / 2 #

Posa # y = -11 / 2 # in # (i) #

#implies 7x-11/2 = -2 # multipliqueu ambdues parts per #2#

# implies14x-11 = -4 #

#implies 14x = 7 #

#implies x = 1/2 #