Solving Simultaneous Equations: -4P1 + 6P2 =54, 5P1 + 4P2=48

[smalls]

so i got this question;

-4P1 + 6P2 =54
5P1 + 4P2=48

and my answer has to be to 3 decimal places.i got abit cofused at a point.but i have worked it out though..it got P1= -1.565 and P2= -13.956...

just need some one who's really good at this to double check it for me..if its wrong,then please let me know ...sorry for adding my workout..too long to do so

 

[Mark44]

I moved your thread from the technical math section to here. Homework-type problems must be posted in the Homework & Coursework section.

so i got this question;

-4P1 + 6P2 =54
5P1 + 4P2=48

and my answer has to be to 3 decimal places.i got abit cofused at a point.but i have worked it out though..it got P1= -1.565 and P2= -13.956...

just need some one who's really good at this to double check it for me..if its wrong,then please let me know ...sorry for adding my workout..too long to do so

Why can't you check it for yourself? Just substitute your values of P1 and P2 into your system. If your solutions are correct, you should get two true statements.

Being as you round your solutions, when you substitute your values, the left sides won't be exactly equal to the right sides, but they shouldn't be too far off.

 

[Mark44]

Copied from the other thread you started.

Homework Statement

-4P1 + 6P2 =54 →eq 1
5P1 + 4P2=48 →eq 2

Homework Equations

well.im really stuck at the the numbers to use to multiply...i plan on eliminating p2,
so i multiplied eq 1 by 2___2×eq 1...and then eq 2 by 3_____3×eq 2

have i started correctly?

The Attempt at a Solution

 

[Mark44]

What does this mean?

i multiplied eq 1 by 2___2×eq 1...and then eq 2 by 3_____3×eq 2

 

[Mark44]

To eliminate the 2nd equation add 5 times the first equation to 4 times the second equation.

 

[SteamKing]

so i got this question;

-4P1 + 6P2 =54
5P1 + 4P2=48

and my answer has to be to 3 decimal places.i got abit cofused at a point.but i have worked it out though..it got P1= -1.565 and P2= -13.956...

just need some one who's really good at this to double check it for me..if its wrong,then please let me know ...sorry for adding my workout..too long to do so

Your solutions are obviously wrong. You have P1 and P2 both as negative numbers. By inspecting the second equation with your purported solutions, they cannot possibly be correct since 48 is positive, and adding two negative numbers can only result in another negative number.

If you provide your calculations, we might be able to figure out where you went wrong.

 

[Chestermiller]

well.im really stuck at the the numbers to use to multiply...i plan on eliminating p2,
so i multiplied eq 1 by 2___2×eq 1...and then eq 2 by 3_____3×eq 2

have i started correctly?

Yes. What do you do next?

 

[adjacent]

so i got this question;

-4P1 + 6P2 =54
5P1 + 4P2=48

and my answer has to be to 3 decimal places.i got abit cofused at a point.but i have worked it out though..it got P1= -1.565 and P2= -13.956...

just need some one who's really good at this to double check it for me..if its wrong,then please let me know ...sorry for adding my workout..too long to do so

Look at this for example,

$2x-3y=20$
$3x+4y=40$

What do you do?
$3(2x-3y)=3(20)$
$2(3x+4y)=2(40)$

Which gives:
$6x-9y=60$
$6x+8y=80$
We can now cancel out 6 by multiplying the whole 2nd equation with -1
Which gives: $-6x-8y=-80$

Then add the two equations together:
$-17y=-20$
$y=\frac{20}{17}$

We have got y, Substitute y in one of the equations and find x:Which gives $x=\frac{200}{17}$

When we substitute x and y in both equations,it should turn out to be true

That's how we usually solve simultaneous equations