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kakasveta [241]
3 years ago
12

If one zero of the following polynomial 8x^2-13x-4k is the reciprocal of the other, then find k

Mathematics
1 answer:
tekilochka [14]3 years ago
4 0

Answer:

k = -2

Step-by-step explanation:

2 way to solve:

1st: 8x²-13x-4k = 8(x²-(13/8)x-(k/2))

if 2 roots: a and 1/a

8(x-a)(x-1/a) = 8(x²-(13/8)x-(k/2))

x²-(a+1/a)x+1 = x²-(13/8)x-(k/2)

1 = -(k/2)

<u>k = -2</u>

<u>2nd:</u> 2 roots of 8x²-13x-4k      x=(-b±√b²-4ac)/2a

x = (13±√169-4*8*(-4k))/16 = (13±√169+128k)/16

(13+(√169+128k))/16 = 16/ (13-(√169+128k))  ... root1=1/root2

(13+(√169+128k))*(13-(√169+128k)) = 16*16

13² - (√169+128k)² = 256

169-169-128k = 256

-128k = 256

k = -2

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