How do you solve y=|x|y=|x| and y=1/2x+4y=12x+4 using substitution?

1 Answer
Feb 12, 2018

(x,y)=(8,8)(x,y)=(8,8) or (x,y)=(-8/3,8/3)(x,y)=(83,83)

Explanation:

Given
[1]color(white)("XXX")y=abs(x)XXXy=|x|
[2]color(white)("XXX")y=1/2x+4XXXy=12x+4

Substituting abs(x)|x| for yy (based on [1])
in [2], we get:
[3]color(white)("XXX")abs(x)=1/2x+4XXX|x|=12x+4

which implies:
{: ("either ",[4]color(white)("xx")-x=1/2x+4," or ",[8]color(white)("xx")x=1/2x+4), (,rarr[5]color(white)("xx")-3/2x=4,,rarr[9]color(white)("xx")1/2x=4), (,rarr[6]color(white)("xx")x=-8/3,,rarr[10]color(white)("xx")x=8), ("then based on [1]",,,), (,rarr[7]color(white)("xx")y=8," or ",rarr[11]color(white)("xx")y=8/3) :}