SOLUTION: What adds to give you '+90' and multiplies to give you '-7200'?

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Question 340042: What adds to give you '+90' and multiplies to give you '-7200'?
Answer by Edwin McCravy(20054)   (Show Source): You can put this solution on YOUR website!
What adds to give you '+90' and multiplies to give you '-7200'?

Let the two numbers be x and y

Then 

x + y = 90
   xy = -7200

Solve the first for y:

y = 90 - x

Substitute in the other equation:

  x(90 - x) = -7200

  90x - x² = -7200

-x² + 90x + 7200 = 0

 x² - 90x - 7200 = 0

Solve by the quadratic formula:

















  




Since the equations 

x + y = 90
   xy = -7200

are symmetrical in x (the same if x and y are interchanged)

the two solutions are the values of x and y

So the answers are

 and  

-------------------------

Checking to see if they add to +90





Checking to see if they multiply to give -7200









So those are the right answers.

Edwin
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