If $$x+\cfrac{1}{x}=4$$, then $${x}^{4}+\cfrac{1}{{x}^{4}}$$ is equal to
Correct option is B. $$194$$
Given,
$$x+\dfrac{1}{x}=4$$
squaring on both sides, we get,
$$x^2+\dfrac{1}{x^2}+2=16$$
$$x^2+\dfrac{1}{x^2}=16-2=14$$
squaring on both sides, we get,
$$x^4+\dfrac{1}{x^4}+2=196$$
$$x^4+\dfrac{1}{x^4}=196-2=194$$