1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Simultanous Equation

  1. Nov 26, 2013 #1
    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
     
  2. jcsd
  3. Nov 26, 2013 #2

    Mark44

    Staff: Mentor

    I moved your thread from the technical math section to here. Homework-type problems must be posted in the Homework & Coursework section.
    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.
     
  4. Nov 26, 2013 #3

    Mark44

    Staff: Mentor

    Copied from the other thread you started.
     
  5. Nov 26, 2013 #4

    Mark44

    Staff: Mentor

    What does this mean?
     
  6. Nov 26, 2013 #5

    Mark44

    Staff: Mentor

    To eliminate the 2nd equation add 5 times the first equation to 4 times the second equation.
     
  7. Nov 26, 2013 #6

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper


    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.
     
  8. Nov 26, 2013 #7
    Yes. What do you do next?
     
  9. Nov 27, 2013 #8

    adjacent

    User Avatar
    Gold Member

    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
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Simultanous Equation
  1. Simultaneous equations (Replies: 7)

  2. Simultaneous equations (Replies: 3)

  3. Simultaneous equations (Replies: 9)

  4. Simultaneous Equations (Replies: 3)

  5. Simultaneous Equations (Replies: 1)

Loading...