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If (r -8) is a factor of r^2 - kr - 56, then k =

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If (r -8) is a factor of r^2 - kr - 56, then k = [#permalink] New post   08 Nov 2012, 23:46
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66% (01:09) correct 34% (01:28) wrong based on 158 sessions
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If (r -8) is a factor of r^2 - kr - 56, then k =

(A) -15
(B) -10
(C) -1
(D) 1
(E) 10
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D
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Re: If (r -8) is a factor of r^2 - kr - 56, then k = [#permalink] New post   09 Nov 2012, 01:08
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Pansi wrote:
If (r -8) is a factor of r2 - kr - 56, then k =
(A) -15
(B) -10
(C) -1
(D) 1
(E) 10

if second factor is n then
8n = -56 => n = -7
Also, 8+n = -k
=> k =-1

Ans C it is.
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Re: If (r -8) is a factor of r^2 - kr - 56, then k = [#permalink] New post   09 Nov 2012, 03:43
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Pansi wrote:
If (r -8) is a factor of r2 - kr - 56, then k =
(A) -15
(B) -10
(C) -1
(D) 1
(E) 10


Other root = \(\frac{-56}{8}\) \(= -7\)

Sum of roots = 8-7 = 1 = -(-k) = k

k=1. Answer is D.

Kudos Please if my post helped.
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Re: If (r -8) is a factor of r^2 - kr - 56, then k = [#permalink] New post   10 Nov 2014, 02:01
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Pansi wrote:
If (r -8) is a factor of r^2 - kr - 56, then k =

(A) -15
(B) -10
(C) -1
(D) 1
(E) 10


Similar question to practice: if-t-8-is-a-factor-of-t-2-kt-48-then-k-166573.html
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Re: If (r -8) is a factor of r^2 - kr - 56, then k = [#permalink] New post   12 Nov 2014, 02:05
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\(r^2 - kr - 56\)

r-8 is already a factor

Other factor has to be 7, +ve which is (r+7)

\((r-8)(r+7) = r^2 - 1r -56\)

Comparing above equation with the given equation

-k = -1

k =1

Answer = D
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Re: If (r -8) is a factor of r^2 - kr - 56, then k = [#permalink] New post   03 Feb 2016, 09:48
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We know that (r-8) is a factor, therefore 8 is a ZERO of the polynomial. Just plug in 8, set equal to zero, and solve for k.

64-8k - 56 = 0.
8 - 8k = 0.
k = 1.
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Re: If (r -8) is a factor of r^2 - kr - 56, then k = [#permalink] New post   16 Oct 2022, 00:08
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Re: If (r -8) is a factor of r^2 - kr - 56, then k = [#permalink]
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