Đáp án:
$B = -76$
Giải thích các bước giải:
$B = \left(\dfrac{4}{\sqrt3 +1} + \dfrac{1}{\sqrt3 -2} - \dfrac{6}{3 -\sqrt3}- \dfrac{1}{\sqrt5 -2}\right)\cdot\left(9-\sqrt5\right)$
$\to B = \left[\dfrac{4\left(\sqrt3 -1\right)}{\left(\sqrt3 +1\right)\left(\sqrt3 -1\right)} + \dfrac{\sqrt3 +2}{\left(\sqrt3 -2\right)\left(\sqrt3 + 2\right)} - \dfrac{6\left(3+\sqrt3\right)}{\left(3 -\sqrt3\right)\left(3+\sqrt3\right)}- \dfrac{\sqrt5 +2}{\left(\sqrt5 -2\right)\left(\sqrt5 +2\right)}\right]\cdot\left(9-\sqrt5\right)$
$\to B = \left[2\left(\sqrt3 -1\right)-\left(\sqrt3 + 2\right) - \left(3+\sqrt3\right)- \left(\sqrt5 +2\right)\right]\cdot\left(9-\sqrt5\right)$
$\to B = \left(-9-\sqrt5\right)\cdot\left(9-\sqrt5\right)$
$\to B = \left(-\sqrt5\right)^2 - 9^2$
$\to B = -76$
