# How do you solve x+y = 4 and 5x-2y = -1?

Jun 1, 2015

Starting with $x + y = 4$, subtract $x$ from both sides to get:

$y = 4 - x$

Then substitute this in the second equation as follows:

$- 1 = 5 x - 2 y$

$= 5 x - 2 \left(4 - x\right) = 5 x - 8 + 2 x = 7 x - 8$

Add $8$ to both ends to get:

$7 x = 7$

Divide both sides by $7$ to get

$x = 1$

Substitute that value for $x$ into $y = 4 - x$ to get

$y = 4 - x = 4 - 1 = 3$