How do you solve by substitution #x-y+-15# and #x+y=-5#?

1 Answer
Jun 5, 2015

Assuming the first component should have (#=-#) instead of (#+-#)

[1]#color(white)("XXXX")##x-y = -15#
[2]#color(white)("XXXX")##x+y=-5#

Rearranging the terms of [1]
[3]#color(white)("XXXX")##x= y-15#

Substituting #(y-15)# for #x# into [2]
[4]#color(white)("XXXX")##(y-15) + y = -5#
[5]#color(white)("XXXX")##y=5#

Substituting #5# for #y# back in [1]
[6]#color(white)("XXXX")##x - 5 = -15#
[7]#color(white)("XXXX")##x = -10#

Solution: #(x,y) = (-10,5)#