How do you solve the following system?: #3x+3y=-21 , 4x-3y=15 #

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Answer 1 · 2016-06-04T22:08:23

#x=-6/7, y=-129/12#

use the addition/elimination method to solve for x.

#3x+3y=-21#
#4x-3y=15#

3x + 4x = 7x, 3y - 3y = 0 and -21 + 15 = -6

#:.7x=-6# so #x=-6/7#

sub in and test

#3(-6/7)+3y=-21#
#-18/7+3y=-21#

multiply everything by 7 to eliminate the fraction

#-18+21y=-147#

#21y=-129#

#y=-129/12#

.

#4(-6/7)-3y=15#
#-24/7-3y=15#

multiply everything by 7 to eliminate the fraction

#-24-21y=105#

#-21y=129#

#y=-129/12#