Question

Answer 1

    

Answer 2

Giới hạn \(\lim\limits_{x\rightarrow1}\dfrac{f\left(x\right)-12}{x-1}\) hữu hạn \(\Rightarrow f\left(x\right)-12=0\) có nghiệm \(x=1\)

\(\Rightarrow f\left(1\right)-12=0\Rightarrow f\left(1\right)=12\)

\(\lim\limits_{x\rightarrow1}\dfrac{f\left(x\right)-12}{x-1}.\dfrac{1}{\sqrt{5f\left(x\right)+4}+8}=30.\dfrac{1}{\sqrt{5.f\left(1\right)+4}+8}=\dfrac{30}{\sqrt{5.12+4}+8}=...\)