Science

Math

Humanities

... and beyond

Socratic Meta
Featured Answers

Topics

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

1 Answer

Mar 14, 2018

$(x,y)=(18,-52)$

Explanation:

Given
[1] $color(white)("XXX")3x+y=2$
[2] $color(white)("XXX")4x+y=20$

We can re-arrange [1] into the form:
[3] $color(white)("XXX")y=2-3x$

Then we can substitute (as requested) $(2-3x)$ for $y$ in [2]
[4] $color(white)("XXX")4x+(2-3x)=20$

Simplifying [4]
[5] $color(white)("XXX")x+2=20$

The subtracting $2$ from both sides of [5]
[6] $color(white)("XXX")x=18$

Based on [6], we can now substitute $18$ for $x$ in [1]
[7] $color(white)("XXX")3 * 18 +y=2$

With some simplification
[8] $color(white)("XXX")54+y=2$

[9] $color(white)("XXX")y=-52$

Related questions

See all questions in Systems Using Substitution

Impact of this question

7046 views around the world

You can reuse this answer
Creative Commons License