12. (-8)= (-25).(-4)=
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a) (12 + 8) x 4 = 20 x 4
= 80
12 + 8 x 4 = 12 + 32
= 44
b) 25 + 75 : 5 = 25 + 15
= 40
(25 + 75) : 5 = 100 : 5
= 20

1,-(4+7)=(-4-7)
2,-(12-25)=(-12+25)
3,-(-8+7)=(8-7)
4,+(-15-4)=(-15-4)
5,+(23-12)=(23-12).

a) \( - \left( {4 + 7} \right) = - 11\)
\(\begin{array}{l}\left( { - 4 - 7} \right) = \left( { - 4} \right) + \left( { - 7} \right)\\ = - \left( {4 + 7} \right) = - 11\\ \Rightarrow \left( { - 4 - 7} \right) = - \left( {4 + 7} \right)\end{array}\)
b)
\(\begin{array}{l} - \left( {12 - 25} \right) = - \left[ {12 + \left( { - 25} \right)} \right]\\ = - \left[ { - \left( {25 - 12} \right)} \right] = - \left( { - 13} \right) = 13\end{array}\)
\(\begin{array}{l}\left( { - 12 + 25} \right) = 25 - 12 = 13\\ \Rightarrow - \left( {12 - 25} \right) = \left( { - 12 + 25} \right)\end{array}\)
c)
\(\begin{array}{l} - \left( { - 8 + 7} \right) = - \left[ { - \left( {8 - 7} \right)} \right] = - \left( { - 1} \right) = 1\\\left( {8 - 7} \right) = 1\\ \Rightarrow - \left( { - 8 + 7} \right) = \left( {8 - 7} \right)\end{array}\)
d)
\(\begin{array}{l} + \left( { - 15 - 4} \right) = + \left[ {\left( { - 15} \right) + \left( { - 4} \right)} \right]\\ = + \left[ { - \left( {15 + 4} \right)} \right] = + \left( { - 19} \right) = - 19\\\left( { - 15 - 4} \right) = \left( { - 15} \right) + \left( { - 4} \right)\\ = - \left( {15 + 4} \right) = - 19\\ \Rightarrow + \left( { - 15 - 4} \right) = \left( { - 15 - 4} \right)\end{array}\)
e)
\(\begin{array}{l} + \left( {23 - 12} \right) = + 11 = 11\\\left( {23 - 12} \right) = 11\\ \Rightarrow + \left( {23 - 12} \right) = \left( {23 - 12} \right)\end{array}\)

a, (-4) . 125 . (-25) . (-11) . (-8)
= [(-4) . (-25)] . {[125 . (-8)] . (-11)}
= 100 . 11000 = 1100000
b, (-42) . 25 . (-25) . (-5) . (-4)
= [(-42) . (-5)] . [25 . (-4)] . 25
= 210 . (-100) . 25
= -5025000

Ta có: \(\frac{4^6.25^5-2^{12}.25^4}{2^{12}.5^8-10^8.64}=\frac{2^{12}.5^{10}-2^{12}.5^8}{2^{12}.5^8-2^8.5^8.2^6}\)
\(=\frac{2^{12}.\left(5^{10}-5^8\right)}{2^{12}.5^8-2^{14}.5^8}\)
\(=\frac{2^{12}.5^8.\left(5^2-1\right)}{5^8.\left(2^{12}-2^{14}\right)}\)
\(=\frac{2^{12}.5^8.24}{5^8.2^{12}.\left(1-2^2\right)}\)
\(=\frac{24}{-3}\)
\(=-8\)
Học "tuốt" nha^^

a: \(=\dfrac{5}{6}\cdot\dfrac{-12}{7}=\dfrac{-10}{7}\)
b: \(=\dfrac{7}{8}\cdot\dfrac{8}{14}=\dfrac{7}{14}=\dfrac{1}{2}\)
c: \(=\dfrac{4}{5}\cdot\dfrac{-15}{8}=\dfrac{-3}{2}\)
d: \(=\dfrac{15}{16}\cdot\dfrac{8}{25}=\dfrac{15}{25}\cdot\dfrac{1}{2}=\dfrac{3}{5}\cdot\dfrac{1}{2}=\dfrac{3}{10}\)
đ: \(=\dfrac{2}{3}-\dfrac{70}{175}=\dfrac{2}{3}-\dfrac{2}{5}=\dfrac{10-6}{15}=\dfrac{4}{15}\)

25 . { 32 : [ 12 - 4 + 4 . ( 16 : 8 ) = 25 . { 32 : [ 12 - 4 + 4 .2) = 25 . { 32 :20) = 25* 1.6 = 40