How do solve the following linear system?: # x+y=-4, 2x + 4y = 8 #?

2 Answers
Aug 4, 2018

Answer:

#x=-12 and y=8#

Explanation:

Here ,

#x+y=-4#

#:.y=-x-4.....to(1)#

#2x+4y=8...........to(2)#

Subst. #y=-x-4# into #(2)#, we get

#2x+4(-x-4)=8#

#:.2x-4x-16=8#

#:.-2x=16+8#

#:.-2x=24#

#:.color(blue)(x=-12#

Subst.# x=-12# into #(1)#

#y=-(-12)-4=12-4#

#:.color(blue)(y=8#

Hence , #x=-12 and y=8#

Aug 4, 2018

Answer:

#x=-12 #
#y=8#

Explanation:

#x+y=-4# so #x=-4-y#

Substitute this into the second equation

#2x+4y=8 =>2(-4-y)+4y=8#

Multiply out the bracket

#-8-2y+4y=8#

Add 8 to both sides

#2y=16#

Divide by 2

#y=8#

Now put #y=8# into # x+y=-4#

#x+8=-4#

Subtract 8 from both sides

#x=-12#