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Mathematics
Problem
For what values of
k
k
k
is the function
f
(
x
)
=
1
x
2
+
k
x
+
9
f(x)=\dfrac{1}{\sqrt{x^{2}+kx+9}}
f
(
x
)
=
x
2
+
k
x
+
9
1
defined for all real
x
x
x
? a)
∣
k
∣
≤
6
|k|\le 6
∣
k
∣
≤
6
b)
k
=
−
6
or
k
=
6
k=-6\text{ or }k=6
k
=
−
6
or
k
=
6
c)
∣
k
∣
<
6
|k|<6
∣
k
∣
<
6
d)
∣
k
∣
>
6
|k|>6
∣
k
∣
>
6
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