Results 1 to 3 of 3

Math Help - May someone solve this equations for me?

  1. #1
    Newbie
    Joined
    Feb 2009
    Posts
    1

    May someone solve this equations for me?

    X+5y=21
    x+3y=11


    3x+y=13
    5x+2y=7
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member TheMasterMind's Avatar
    Joined
    Dec 2008
    Posts
    155
    Quote Originally Posted by thebesta1 View Post
    X+5y=21
    x+3y=11


    3x+y=13
    5x+2y=7
    x+5y=21
    x+3y=11

    x=21-5y (isolate x)

    sub the value of x to 2nd equation to solve for y

    21-5y+3y=11

    -2y=-10

    y=5

    substitute the value of y into the other equation to solve for x

    x+5(5)=21

    x+25=21

    x=-4

    Do you see what I did? Now follow the same method for solving the second one and show me what you get
    Last edited by TheMasterMind; February 11th 2009 at 06:22 PM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member
    Joined
    Jan 2009
    Posts
    591
    Quote Originally Posted by thebesta1 View Post
    X+5y=21
    x+3y=11


    3x+y=13
    5x+2y=7
    from this
    1x + 5y = 21
    1x + 3y = 11

    1 5
    1 3

    1*3 - 1*5 = 3-5 = -2
    the determinant of the equation

    Then find the determinant of a replacement:
    replace the constants of the variable x:

    21 5
    11 3

    21*3 - 11-5 = 63 - 55 = 8

    Then divide this determinant with the system determinant:

    8 / -2 = -4

    Thus x = -4

    Then do the same and replace the constant of y:

    1 21
    1 11

    1*11 - 21*1 = 11 - 21 = -10

    -10 / -4 = 2.5
    thus y = 2.5
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. equations solve
    Posted in the Differential Equations Forum
    Replies: 3
    Last Post: September 30th 2011, 07:46 AM
  2. Is it possible to solve these equations?
    Posted in the Calculus Forum
    Replies: 2
    Last Post: June 8th 2011, 03:43 PM
  3. Solve the following equations for 0<x<360 ?
    Posted in the Trigonometry Forum
    Replies: 4
    Last Post: January 31st 2011, 01:33 AM
  4. Equations - Can't solve it!
    Posted in the Algebra Forum
    Replies: 3
    Last Post: January 22nd 2009, 03:22 AM
  5. solve equations
    Posted in the Algebra Forum
    Replies: 2
    Last Post: September 9th 2008, 08:04 PM

Search Tags


/mathhelpforum @mathhelpforum