Question

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

Answer 1

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.