# Solve the system of linear equations

40x1+ 30x2= 24
20x1+ 15x2= -14

#### Subhotosh Khan

##### Super Moderator
Staff member
40x1+ 30x2= 24
20x1+ 15x2= -14

Where are you stuck?

You have 100+ posts -- you should know that you need to show us your efforts before we put in our efforts to help you solve your problem.

#### frctl

##### Junior Member
I think I must solve by back substitution but I think I am must reduce first

#### Subhotosh Khan

##### Super Moderator
Staff member
I think I must solve by back substitution but I think I am must reduce first

We will start discussion from there.

#### frctl

##### Junior Member
I don't see any common factor, can I instead add both equations together?

#### Subhotosh Khan

##### Super Moderator
Staff member
I don't see any common factor, can I instead add both equations together?
What method you are trying to apply? - matrix? substitution? elimination? something else?

#### frctl

##### Junior Member
I can use any, I am asked simply to solve

#### Subhotosh Khan

##### Super Moderator
Staff member
I can use any, I am asked simply to solve
So use one of those and show us the work!

#### frctl

##### Junior Member
40x1+ 30x2= 24
20x1+ 15x2= -14

Multiply equation 2 by 2
40x1+ 30x2= 24
40x1 + 30x2 = -28

Adding both equations gives me -4

#### Subhotosh Khan

##### Super Moderator
Staff member
40x1+ 30x2= 24
20x1+ 15x2= -14

Multiply equation 2 by 2
40x1+ 30x2= 24
40x1 + 30x2 = -28

Adding both equations gives me -4................................Incorrect
Try again!

However, addition will not guide you towards a valid conclusion.

#### frctl

##### Junior Member
What can I do in the place?

Maybe I can isolate x1

#### Subhotosh Khan

##### Super Moderator
Staff member
What can I do in the place?
Did you figure out:

What mistake did you make in your response #9?

You are adding two sets of equations - the result should an equation (not a number).

First correct your mistake - then we will discuss "what you can do in its place".

#### frctl

##### Junior Member
40x1+ 30x2= 24
20x1+ 15x2= -14

Multiply equation 2 by 2
40x1+ 30x2= 24
40x1 + 30x2 = -28

#### Subhotosh Khan

##### Super Moderator
Staff member
40x1+ 30x2= 24
20x1+ 15x2= -14

Multiply equation 2 by 2
40x1+ 30x2= 24
40x1 + 30x2 = -28
Next - what operation did you conduct?

#### frctl

##### Junior Member
I isolated x1
x1 = (-30x2+24)/40

#### Subhotosh Khan

##### Super Moderator
Staff member
I isolated x1
x1 = (-30x2+24)/40

#### frctl

##### Junior Member
I can't edit this response anymore.
Is there another mistake?

#### Subhotosh Khan

##### Super Moderator
Staff member
I can't edit this response anymore.
Is there another mistake?
Redo your response #9 with "corrected" steps.

#### frctl

##### Junior Member
I don't understand what do you mean

#### Subhotosh Khan

##### Super Moderator
Staff member
I don't understand what do you mean
What part of my statement you do not understand?

While writing response #9 - you conducted some mathematical steps and you made a conclusion (which was incorrect).

I would like for you to "find" your mistake and correct your conclusion (in a new post - since you cannot edit it).