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

1 Answer
Apr 18, 2017

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.