How do you solve the system #x=-4y# and #3x+2y=20# using substitution?

1 Answer
Oct 15, 2016

Answer:

#(x,y)=(8,-2)#

Explanation:

Given
#color(white)("XXX")color(red)x=color(red)(-4y)#
and
#color(white)("XXX")3color(red)x+2y=20#

Substituting #color(red)(""(-4y))# for #color(red)x# into the second equation:
#color(white)("XXX")3 * color(red)(""(-4y))+2y =20#

#color(white)("XXX")-12 y +2y =20#

#color(white)("XXX")-10y=20#

#color(white)("XXX")color(blue)y=color(blue)(-2)#

Now substitute #color(blue)(""(-2))# for #color(blue)y# back in the original equation #x=-4color(blue)y#

#color(white)("XXX")x=-4 * color(blue)(""(-2))#

#color(white)("XXX")x=8#