Monday

September 1, 2014

September 1, 2014

Posted by **rob** on Friday, January 2, 2009 at 3:17pm.

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 -
**Reiny**, Friday, January 2, 2009 at 3:28pmIt 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 -
**Damon**, Friday, January 2, 2009 at 3:28pmfrom 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)

**Related Questions**

Geometry HELP!!! - What happens to the graph of the line y = 3x -2 when the ...

Algebra - To solve the system of equations, which expression could be ...

Algebra - I have some problems that I am having trouble with and I have some ...

Math - Solve the system using any algebraic method. 2x - 2y + z = 3 5y - z = -31...

Algebra - I have a few questions that I need help with. Solve the radical ...

Substitution Method-Plz help - Use the Substitution method to solve the system ...

ALGEBRA 1!PLZ HELP! - Use the Substitution method to solve the system of ...

Algebra Multiple Choice - Hello, This is the last of questions I have for my ...

TO DRWLS/MATH HELP PLEASE - How do i solve inequalitites with three variables. I...

algebra - im trying to solve a literal equation, then solve the specific ...