the range of the function f(k)=k2+2k+1 is (25,64). what is the functions domain

1.  Set f(k) = 25

k² + 2k + 1 = 25 

k² + 2k - 24 = 0

(k - 4)(k + 6) = 0

So two limiting values in the domain are -4 and 6

2. Set f(k) = 64

k² + 2k + 1 = 64

k² + 2k - 63 = 0

(k - 7)(k + 9) = 0

So the other two limits are -9 and 7

The domain is  [-9, -4] ∪ [6, 7]

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