Đáp án:

Bài 1 :

$B = \frac{76}{75}$

Bài 2 :

\(\left[ \begin{array}{l}x=\frac{68}{45}\\x=-\frac{76}{45}\end{array} \right.\)

Giải thích các bước giải:

Bài 1 :

$B = \frac{0,8:(\frac{4}{5}.125)}{0,64-\frac{1}{25}} + \frac{(1,08-\frac{2}{25}):\frac{4}{7}}{(6\frac{5}{9}-3\frac{1}{4}).2\frac{3}{17}} + ( 1,2.0,5 ) : \frac{4}{5}$

$⇔ B = \frac{0,8:(4.25)}{0,64-\frac{4}{100}} + \frac{(1,08-\frac{8}{100}):\frac{4}{7}}{(\frac{59}{9}-\frac{13}{4}).\frac{36}{17}} + 0,6 : \frac{4}{5}$

$⇔ B = \frac{0,8:100}{0,64-0,04} + \frac{(1,08-0,08).\frac{7}{4}}{(\frac{236}{36}-\frac{117}{36}).\frac{36}{17}} + \frac{6}{10} . \frac{5}{4}$

$⇔ B = \frac{0,008}{0,6} + \frac{1.\frac{7}{4}}{\frac{119}{36}.\frac{36}{17}} + \frac{3}{5}.\frac{5}{4}$

$⇔ B = \frac{\frac{8}{1000}}{\frac{6}{10}} + \frac{\frac{7}{4}}{7} + \frac{3}{4}$

$⇔ B = \frac{8}{1000} . \frac{10}{6} + \frac{1}{4} + \frac{3}{4}$

$⇔ B = \frac{80}{6000} + \frac{4}{4}$

$⇔ B = \frac{80}{80.75} + 1$

$⇔ B = \frac{1}{75} + 1$

$⇔ B = \frac{1+75}{75}$

$⇔ B = \frac{76}{75}$

Bài 2 :

$| x + \frac{4}{45} | - | - 3,75 | = - | - 2,15 |$

$⇔ | x + \frac{4}{45} | - 3,75 = - 2,15$

$⇔ | x + \frac{4}{45} | = - 2,15 + 3,75$

$⇔ | x + \frac{4}{45} | = 1,6$

$⇔ | x + \frac{4}{45} | = \frac{16}{10}$

$⇔ | x + \frac{4}{45} | = \frac{8}{5}$

$⇔ | x + \frac{4}{45} | = \frac{72}{45}$

⇔ \(\left[ \begin{array}{l}x+\frac{4}{45}=\frac{72}{45}\\x+\frac{4}{45}=-\frac{72}{45}\end{array} \right.\)

⇔ \(\left[ \begin{array}{l}x=\frac{72}{45}-\frac{4}{45}\\x=-\frac{72}{45}-\frac{4}{45}\end{array} \right.\)

⇔ \(\left[ \begin{array}{l}x=\frac{68}{45}\\x=-\frac{76}{45}\end{array} \right.\)