SOLUTION: Find all integers k such that the trinomial is a perfect square trinomial 64x(squared) + kxy + y (squared) So am I just replacing k ?

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Question 686945: Find all integers k such that the trinomial is a perfect square trinomial
64x(squared) + kxy + y (squared)
So am I just replacing k ?

Found 3 solutions by MathLover1, stanbon, Edwin McCravy:
Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!

Perfect Square Trinomials: These are of the form %28x%2By%29%5E2+=+%28x%2By%29%28x%2By%29+=+x%5E2+%2B2xy%2By%5E2
given:
64x%5E2+%2B+k%2Axy+%2B+y+%5E2
%288x%29%5E2+%2B+k%2Axy+%2B+1%2Ay+%5E2 ....using a Rule for the Square of a Sum (a + b) ^2 = a ^2 + 2ab + b ^2, where a=8 and b=1 we can find k
and it is 2%2A8%2A1=16
%288x%29%5E2+%2B+16xy+%2B+y+%5E2
%288x+%2B+y%29%5E2
%288x+%2B+y%29%288x+%2B+y%29

Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
Find all integers k such that the trinomial is a perfect square trinomial
64x(squared) + kxy + y (squared)
So am I just replacing k ?
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Yes, solve for "k":
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Your Problem:
(8x)^2 + kxy + y^2
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Perfect Square Form: a^2 + 2ab + b^2
Your Problem:
a = 8x ; b = y
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Middle term has to be 2ab = 2(8x)y = 16xy
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So k has to be 16
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Cheers,
Stan H.
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Answer by Edwin McCravy(20054) About Me  (Show Source):
You can put this solution on YOUR website!

The other tutors did not mention that there are two answers.
The problem did not state that k must be a POSITIVE integer.  It
just stated that k must be an integer, and an integer can be
POSITIVE or NEGATIVE.  So we must give both answers.

If 64x² + kxy + y²

is a perfect square it will have to factor as

either  (8x + y)² or as (8x - y)²

If it factors as (8x + y)², then that is the same as

(8x + y)(8x + y) = 64x² + 16xy + y².  In that case the

middle term +kxy would equal to +16xy and so k would be 16.

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If it factors as (8x - y)², then that is the same as

(8x - y)(8x - y) = 64x² - 16xy + y².  In that case the

middle term +kxy would equal to -16xy and so k would be -16.

Answer: Two possibilities: k = 16, k = -16

Edwin