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What two numbers add to 18 and multiply to 82
asked
Dec 20, 2017
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What two numbers add to 18 and multiply to 82
Mathematics
high-school
Avinash B
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Avinash B
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2
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4
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The two numbers that add to 18 and multiply to 82 are
9 + i and 9 - i
.
(9 + i)(9 - i) = 9^2 - i^2 = 81 - (-1) = 81 + 1 =
82
(9 + i) + (9 - i) = 9 + i + 9 - i = 9 + 9 + i - i =
18
Noishe
answered
Dec 22, 2017
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Noishe
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The answers are complex numbers...
Here's why...
---------
p+q=18
pq=82
---------
Therefore:
p=18-q
p=82/q
------------
Therefore:
18-q=82/q
q(18-q)=q(82/q)
18q-q²=82
(-1)(18q-q²)=82(-1)
q²-18q=-82
(q-9)²-9²=-82
(q-9)²-81=-82
(q-9)²=-82+81
(q-9)²=-1
q-9=-√(-1)=-i
q-9=√(-1)=i
-----------
Therefore:
q=9-i
q=9+i
-------------
ANSWERS:
When q=9-i, p=9+i
When q=9+i, p=9-i
-----------
Proof:
p+(9-i)=18
p+9-i=18
p=18-9+i
p=9+i
....
p+(9+i)=18
p+9+i=18
p=18-9-i
p=9-i
--------------
More proofs:
p=82/(9+i)
p=(82/(9+i))*((9-i)/(9-i))
p=(82(9-i))/(81-9i+9i-i²)
p=(82(9-i))/(81-(-1))
p=(82(9-i))/82
p=9-i
---------------
p=82/(9-i)
p=(82/(9-i))*((9+i)/(9+i))
p=(82(9+i))/(81+9i-9i-i²)
p=(82(9+i))/(81-(-1))
p=(82(9+i))/82
p=9+i
Roi
answered
Dec 24, 2017
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Roi
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