lisa70 lisa70
  • 23-03-2016
  • Mathematics
contestada

What two numbers multiply to -15 and can also add up to -7

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Аноним Аноним
  • 23-03-2016
Let the numbers be x and y
According to the data : xy=-15 and x+y=-7
xy=-15
x+y=-7

y=-7-x
x(-x-7)=-15

y=-7-x
-x^2-7x=-15

y=-7-x
x^2+7x-15=0

y=-7-x
x=(-7±sqrt(7*7+4*15))/2

y=-7-x
x=(-7±sqrt(109))/2

Goes to two systems.
 1) 
y=-7-x
x=(-7+sqrt(109))/2


y=-7+3.5-sqrt(109))/2
x=(-7+sqrt(109))/2

y=-3.5-sqrt(109))/2
x=(-7+sqrt(109))/2

2)
y=-7-x
x=(-7-sqrt(109))/2

y=-7+3.5+sqrt(109))/2
x=(-7-sqrt(109))/2

y=-3.5+sqrt(109))/2
x=(-7-sqrt(109))/2
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