Đáp án: $B=-\dfrac{196}{19}$
Giải thích các bước giải:
Ta có $\sqrt{x}=\dfrac45\to x=\left(\dfrac45\right)^2=\dfrac{16}{25}$
$\to B=\left(\dfrac{2\cdot \dfrac{16}{25}+9}{\dfrac{16}{25}\cdot \dfrac45-1}+\dfrac{1}{1-\dfrac45}\right):\left(1-\dfrac{\dfrac{16}{25}-2}{\dfrac{16}{25}+\dfrac45+1}\right)$
$\to B=\dfrac{-\dfrac{1285}{61}+5}{\dfrac{95}{61}}$
$\to B=-\dfrac{196}{19}$