# How do you solve the system 2x+7y=3  and x = 1-4y by substitution?

May 24, 2015

Try this:

May 24, 2015

Substitute the formula for $x$ from the second equation into the first equation as follows:

$3 = 2 x + 7 y = 2 \left(1 - 4 y\right) + 7 y = 2 - 8 y + 7 y = 2 - y$

Add $y$ to both ends to get:

$y + 3 = 2$

Subtract #3 from both sides to get:

$y = - 1$

Substitute this value for $y$ into the original second equation to find $x$:

$x = 1 - 4 y = 1 - 4 \left(- 1\right) = 1 + 4 = 5$