Science

Math

Humanities

... and beyond

Socratic Meta
Featured Answers

Topics

How do you solve the system $x = - 4 y$ $x=-4y$ and $3 x + 2 y = 20$ $3x+2y=20$ using substitution?

1 Answer

Oct 15, 2016

$(x, y) = (8, - 2)$ $(x,y)=(8,-2)$

Explanation:

Given
$XXX x = - 4 y$ $color(white)("XXX")color(red)x=color(red)(-4y)$
and
$XXX 3 x + 2 y = 20$ $color(white)("XXX")3color(red)x+2y=20$

Substituting $(- 4 y)$ $color(red)(""(-4y))$ for $x$ $color(red)x$ into the second equation:
$XXX 3 \cdot (- 4 y) + 2 y = 20$ $color(white)("XXX")3 * color(red)(""(-4y))+2y =20$

$XXX - 12 y + 2 y = 20$ $color(white)("XXX")-12 y +2y =20$

$XXX - 10 y = 20$ $color(white)("XXX")-10y=20$

$XXX y = - 2$ $color(white)("XXX")color(blue)y=color(blue)(-2)$

Now substitute $(- 2)$ $color(blue)(""(-2))$ for $y$ $color(blue)y$ back in the original equation $x = - 4 y$ $x=-4color(blue)y$

$XXX x = - 4 \cdot (- 2)$ $color(white)("XXX")x=-4 * color(blue)(""(-2))$

$XXX x = 8$ $color(white)("XXX")x=8$

Related questions

See all questions in Systems Using Substitution

Impact of this question

3389 views around the world

You can reuse this answer
Creative Commons License