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# If f(x) = x^2 + 4 and f(2k) = 36, then which of the following is one

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Re: If f(x) = x^2 + 4 and f(2k) = 36, then which of the following is one [#permalink]
Top Contributor
Given that f(x) = $$x^2$$ + 4 and f(2k) = 36 and we need to find one possible value of k

To find f(2k) we need to compare what is inside the bracket () * in f(2k) and f(x)

=> We need to substitute x with 2k in f(x) = $$x^2$$ + 4 to get the value of f(2k)

=> f(2k) = $$(2k)^2$$ + 4 = $$4k^2$$ + 4 = 36 (given)
=> $$4k^2$$ = 36-4 = 32
=> $$k^2$$ = $$\frac{32}{4}$$ = 8
=> k = $$\sqrt{8}$$ = $$2\sqrt{2}$$

So, Answer will be D
Hope it helps!

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Re: If f(x) = x^2 + 4 and f(2k) = 36, then which of the following is one [#permalink]
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