Algebra

posted by .

I have to solve the following equation:

x+y=9
xy=54

I changed the first equation to y=9-x to solve for y. I got x(9-x)=54 and then 9x-x^2=54. I then changed 9x-x^2= 54 to -x^2 +9x-54=0. I got stuck around here, can someone explain...

  • Algebra -

    It is a good idea to have your equations start with a positive square term, so switch all the signs
    x^2 - 9x + 54 = 0

    This equation does not have a real solution, if you want the imaginary values of x, use the quadratic formula.

    YOu can see intuitively that there cannot be a real answer.
    both the sum and the product are positve, so both x and y must be positive.
    just mentally form some ordered pairs (x,y) which add up to 9.
    No way will the product reach 54, the largest product you would get is (4.5)(4.5) or 20.25

  • Algebra -

    from the second equation say y = 54/x
    then in the first
    x + 54/x = 9

    x^2 -9 x + 54 = 0
    this quadratic has only complex roots
    x = 9/2 +/-(1/2) sqrt(-135)
    = 9/2 +/- (3/2) sqrt (-15)

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Substitution Method-Plz help

    Use the Substitution method to solve the system of equations. x + y = -4 x - y = 2 solve for x in the second equation. x= y+2 Put that in for x in the first equation: x+y=-4 (y+2) + y = -4 solve for y. Then, x= y+2 i don't get it.How …
  2. ALGEBRA 1!PLZ HELP!

    Use the Substitution method to solve the system of equations. y - 2x = -5 3y - x = 5 Solve the first equation for y. y = 2x-5 Substitute that for y in the second equation and solve for x. Then use the value of x to substitute back …
  3. Algebra

    To solve the system of equations, which expression could be substituted for x into the first equation?
  4. Algebra

    I have a few questions that I need help with. Solve the radical equation, and check all proposed solutions. 5. x- square root 3x-2=4 I don't understand this problem. Solve and check the equation. 10. (x^2+14x+49)^3/4-20=7 would I have …
  5. Algebra

    I have some problems that I am having trouble with and I have some that need checking please. Thanks! Solve the equation. 4. (x+7/4)=2(x-1/6) Find all the value(s) of x that make thedenominator(s) zero. Then solve the equation. 6. …
  6. Algebra

    please help me with this question and check my answers. Solve the problem. A rectangle with width 2x + 5 inches has an area of 2x4 + 9x3 - 12x2 - 79x - 60 square inches. Write a polynomial that represents its length. ( I don't know …
  7. algebra

    I just need a quick check before I hand in my work if you would...Thanks. 1. I am to use the intercepts to graph the equation x+3y=6 I used the formula y=mx+b using 3 and -6 for x I got these as my ordered pairs to graph (3, 1), (-6, …
  8. Math

    Solve the system using any algebraic method. 2x - 2y + z = 3 5y - z = -31 x + 3y + 2z = -21 ______________________ The answer I got for this is ( -26, 6,67) but I know its wrong and I don't know why. Help please >< my work is …
  9. Algebra Multiple Choice

    Hello, This is the last of questions I have for my practice assignment. Again I will put what I got. Thanks for your help. 1.) Solve the system using substitution. Write answer as an ordered pair. 4x+2y=8 -5x-2=y A.) First equation …
  10. algebra

    im trying to solve a literal equation, then solve the specific question first part is stumping me, im to solve for X ax=bx-c this is what I got ax-bx=c, but don't know how to get x by itself

More Similar Questions