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What two numbers add to 9 but multiply to -42
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What two numbers add to 9 but multiply to -42
asked
Jul 28, 2017
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What two numbers add to 9 but multiply to -42
Mathematics
high-school
TheoretiCAL
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TheoretiCAL
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Hi,
x+y = 9 ⇒ x = 9-y
x·y = -42
(9-y)·y = -42
9y-y² = -42
y²-9y-42 = 0 for a = 1, b = -9 e c = -42
Δ = b²-4ac
Δ = (-9)²-4(1)(-42)
Δ = 81+168
Δ = 249
y₁ = (-b+√Δ)/2a = (-(-9)+√249)/2(1) = (9+√249)/2 =
9/2 + √249/2
y₂ = (-b-√Δ)/2a = (-(-9)-√249)/2(1) = (9-√249)/2 = 9/2 - √249/2
For y =
9/2 + √249/2
x+y = 9
x = 9-y
x = 9-(9/2 + √249/2)
x = 9/2 - √249/2
For y = 9/2 - √249/2
x+y = 9
x = 9-y
x = 9-(9/2 - √249/2)
x = 9/2 + √249/2
Answer:
Numbers:
9/2 + √249/2
and
9/2 - √249/2
Jeson Martajaya
answered
Jul 30, 2017
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Jeson Martajaya
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The factors of 42 are 1,42,2,21,3,14,6,7. Non of these add together to get 9. One would have to be positive and the other negative but it still doesn't work.
Yanni Wang
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Aug 1, 2017
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Yanni Wang
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