How do you solve this system of equations: $3 x + y = 5 and - x - y = 1$ $3x + y = 5 and - x - y = 1$ ?

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Answer 1 · 2017-11-08T17:14:24

$x = 3, y = - 4$ $x=3, y=-4$

$3 x + y = 5$ $3x+y=5$ ---- 1
$- x - y = 1$ $-x-y=1$ ---- 2

from equation 2,

$x = - 1 - y$ $x=-1-y$

substitute $x = - 1 - y$ $x=-1-y$ into equation 1

$3 (- 1 - y) + y = 5$ $3(-1-y)+y=5$
$- 3 - 3 y + y = 5$ $-3-3y+y=5$
$- 2 y = 8$ $-2y=8$
$y = - 4$ $y=-4$

substitute $y = - 4$ $y=-4$ into $x = - 1 - y$ $x=-1-y$

$x = - 1 - (- 4)$ $x=-1-(-4)$
$x = 3$ $x=3$

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