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Let f(x) be a differntiable function at x = a with f' (a)=2 and f (a)=4. Then \lim_{x\rightarrow a}\frac{xf(a)-af(x)}{x-a} equals to:
Option: 1 2a +4
Option: 2 4-2a
Option: 3 a+4
Option: 4 2a-4

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\\ f^{\prime}(a)=2, f(a)=4 \\ \lim _{x \rightarrow a} \frac{x f(a)-a f(x)}{x-a} \\ \Rightarrow \lim _{x \rightarrow a} \frac{f(a)-a f^{\prime}(x)}{1} \;\;\;\;\;\mathrm{(L'Hopital\; rule)}\\ =f(a)-a f^{\prime}(a) \\ =4-2 a

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