How do you solve the system by substitution #x – 4y = –19# and #–4x – 5y = 13#?

1 Answer
Apr 18, 2017

Answer:

y=3

Explanation:

You can get "x" by itself in the first equation by adding "4y" to both sides of the equation:

#x-4y+4y=-19+4y#

This should leave you with:

#x=4y-19#

Now you can substitute it into the second equation:

#-4(4y-19)-5y=13#

Distribute the "-4" to the numbers in the parenthesis:

#-16y+76-5y=13#

Combine like terms:

#-21y+76=13#

Subtract 76 from both sides to get "y" by itself:

#-21y+76-76=13-76#

Now divide both sides by "-21":

#(-21y)/-21=(-63)/-21#

You should end up with:

#y=(-63)/-21#

You can change it to a decimal by using a calculator:

y=3.