How do you solve the following system?: #3x -6y =21, -x -3y = -7#

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Answer 1 · 2017-10-08T10:15:59

#x= 7# and #y = 0#

#3x -6y =21# -----------Let this be equation(1), and
# -x -3y = -7# ---------- Let this be equation(2)

From (2), by transposition method, we have :

# -x -3y = -7#

# -x = -7+3y#

# x = 7-3y# ---------------let this be equation (3).

Substitute vale of #x# from equation (3) in equation (1):

#3x -6y =21#

#3(7-3y) -6y =21#

#21 -9y -6y = 21#

#21 - 15y = 21#

#-15 y = 21-21#

#y = 0/-15#

#y =0#

From (3) , we can get value of #x#:

# x = 7-3y#

# x = 7-3(0)#

# x = 7-0#

# x = 7#

therefore we have:

#x= 7# and #y = 0#

Cross check by substituting values of #x#and #y# in equation (2):
# -x -3y = -7#
# -7 -3(0) = -7#
# -7 -0 = -7#
# -7 = -7#