Cho các góc với số đo như sau: \(\widehat {A\,\,} = 180^\circ ,\,\,\widehat {B\,} = 15^\circ ,\,\,\widehat {C\,} = 30^\circ ,\,\,\widehat {D\,} = 95^\circ ,\,\,\widehat {E\,} = 120^\circ ,\,\,\widehat {F\,} = 90^\circ .\)

Trong các góc đó, có bao nhiêu góc tù?

1) a) \(\frac{3}{4} \cdot 26\frac{2}{9} - 38\frac{2}{9} \cdot \frac{3}{4}\)

\( = \frac{3}{4} \cdot \left( {26\frac{2}{9} - 38\frac{2}{9}} \right)\)

\( = \frac{3}{4} \cdot \left( {26 + \frac{2}{9} - 38 - \frac{2}{9}} \right)\)

\( = \frac{3}{4} \cdot \left( { - 12} \right) = - 9.\)

b) \(\frac{2}{7} + \frac{5}{7} \cdot \left( {60\% - 0,25} \right) \cdot {\left( { - 2} \right)^2}\)

\( = \frac{2}{7} + \frac{5}{7} \cdot \left( {\frac{{60}}{{100}} - \frac{{25}}{{100}}} \right) \cdot 4\)

\( = \frac{2}{7} + \frac{5}{7} \cdot 4 \cdot \frac{{35}}{{100}}\)

\( = \frac{2}{7} + \frac{{20}}{7}.\frac{7}{{20}}\)

\[ = \frac{2}{7} + 1\]\[ = \frac{9}{7}\].