16.

\(\lim\dfrac{u_n}{v_n}=+\infty\)

17.

\(SA\perp\left(ABC\right)\Rightarrow SA\perp AB\Rightarrow\Delta SAB\) vuông tại A (B đúng)

\(SA\perp\left(ABC\right)\Rightarrow SA\perp BC\) (C đúng)

\(\left\{{}\begin{matrix}SA\perp\left(ABC\right)\Rightarrow SA\perp BC\\AB\perp BC\left(gt\right)\end{matrix}\right.\) \(\Rightarrow BC\perp\left(SAB\right)\) (D đúng)

18.

Tập hợp điểm cách đều 2 điểm AB cho trước là mặt phẳng trung trực của AB

19.

\(\lim\limits_{x\rightarrow1}\dfrac{x-1}{2x-2}=\lim\limits_{x\rightarrow1}\dfrac{x-1}{2\left(x-1\right)}=\dfrac{1}{2}\)

D. Bị lệch về phía đáy

\(a,CH_2=CH-CH_3+H_2\rightarrow\left(Ni,t^o\right)CH_3-CH_2-CH_3\\ CH\equiv C-CH_3+2H_2\rightarrow\left(Ni,t^o\right)CH_3-CH_2=CH_3\\ b,CH\equiv C-CH_3+H_2\rightarrow\left(\dfrac{Pd}{PbCO_3}\right)CH_2=CH-CH_3\\ c,CH_2=CH-CH_3+Br_2\rightarrow\left(CCl_4\right)CH_2Br-BrCH-CH_3\\ CH\equiv C-CH_3+Br_2\rightarrow\left(CCl_4\right)CH_2Br=BrC-CH_3\)

\(d,CH\equiv C-CH_3+AgNO_3+NH_3\rightarrow AgC\equiv C-CH_3+NH_4NO_3\\ e,CH_2=CH-CH_3+H_2O\rightarrow\left(H^+\right)CH_3-CH_2-CH_2-OH\\ CH\equiv C-CH_3+H_2O\rightarrow\left(H^+\right)CH_2=CH-CH_2-OH\\ f,CH_2=CH-CH_3+HCl_{dư}\rightarrow CH_3-CHCl-CH_3\\ CH\equiv C-CH_3+HCl_{dư}\rightarrow CH_2=CCl-CH_3\)

A

Ta có : \(f\left(2\right)=2a+b-6\)

\(\lim\limits_{x\rightarrow2^+}\dfrac{x-\sqrt{x+2}}{x^2-4}=\lim\limits_{x\rightarrow2^+}\dfrac{x^2-x-2}{\left(x-2\right)\left(x+2\right)\left(x+\sqrt{x+2}\right)}\)  

\(=\lim\limits_{x\rightarrow2^+}\dfrac{x+1}{\left(x+2\right)\left(x+\sqrt{x+2}\right)}=\dfrac{3}{16}\)

\(\lim\limits_{x\rightarrow2^-}x^2+ax+3b=4+2a+3b\) 

H/s liên tục tại điểm x = 2 \(\Leftrightarrow\dfrac{3}{16}=2a+3b+4=2a+b-6\)

Suy ra : \(a=\dfrac{179}{32};b=-5\) => t = a + b = 19/32 . Chọn C