For what values of is the function defined for all real ?

MATHEMATICS · Single correct · A Level · Mathematics · Algebra and Functions · Algebra and Functions

Problem

For what values of kk is the function f(x)=1x2+kx+9f(x)=\dfrac{1}{\sqrt{x^{2}+kx+9}} defined for all real xx? (a) ∣k∣≤6|k|\le 6 (b) k=−6 or k=6k=-6\text{ or }k=6 (c) ∣k∣<6|k|<6 (d) ∣k∣>6|k|>6

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