solve the system of linear equations by substitution -3x+y=1, 4x+y=8

Question

-3x+y=1

4x+y=8 Solve. Linear equation by use of substitution

Answer 1

Hi Elena;

-3x+y=1, 4x+y=8

Let's begin with the first equation...

-3x+y=1

Let's isolate y by adding 3x to both sides...

3x-3x+y=3x+1

y=3x+1

Second equation...

4x+y=8

Let's SUBSTITUTE y with 3x+1...

4x+(3x+1)=8

Let's combine like terms...

7x+1=8

Let's subtract 1 from both sides...

-1+7x+1=8-1

7x=7

Let's divide both sides by 7...

(7x)/7=7/7

x=1

 

Original equations...

-3x+y=1, 4x+y=8

Let's begin with the first equation and plug-in x=1

[(-3)(1)]+y=1

-3+y=1

Let's add 3 to both sides...

3-3+y=1+3

y=4

Second equation, is the result of the value of y identical?

4x+y=8

[(4)(1)]+y=8

4+y=8

-4+4+y=8-4

y=4

YES!!!!