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# Well, this one seems to be straightforward, but there are

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Director
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Well, this one seems to be straightforward, but there are [#permalink]

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12 May 2007, 13:17
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Well, this one seems to be straightforward, but there are some doubts....
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Senior Manager
Joined: 03 May 2007
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12 May 2007, 13:26
you need both statements to solve this one.
2 equations 2 unknowns
Director
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12 May 2007, 13:32
Sergey_is_cool wrote:
you need both statements to solve this one.
2 equations 2 unknowns

But why cannot we guess the values from st1? We've got two sqrds, the difference between which is 16, the first sqrd is greater than the second one: 5^2 - 3^2 = 16. Are there any other sqrds the difference between which can give us 16?
VP
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12 May 2007, 13:42
I would say (C)

a^4-b^4 = (a^2-b^2)(a^2+b^2)

Statement 1

(a^2-b^2)=16

we can plug in but we are still missing (a^2+b^2)

insufficient

Statement 2

(a+b)=8

we are still missing (a^2+b^2)

insufficient

Statement 1&2

Knowing that (a^2-b^2)=(a-b)(a+b)=16

and (a+b)=8

we can plug in and find that (a-b)*8=16

a-b=2 & a+b=8

2b=6

b=3

a=5

Senior Manager
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12 May 2007, 13:43
yeah but you can't just guess numbers you have to have the way to prove that the the equation has only one solution.(It's my guess) Do you have the answer?
VP
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12 May 2007, 13:48
nick_sun wrote:
Sergey_is_cool wrote:
you need both statements to solve this one.
2 equations 2 unknowns

But why cannot we guess the values from st1? We've got two sqrds, the difference between which is 16, the first sqrd is greater than the second one: 5^2 - 3^2 = 16. Are there any other sqrds the difference between which can give us 16?

please note that a & b don't have to be integers !!!!!

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# Well, this one seems to be straightforward, but there are

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