Đáp án:
\(\begin{array}{l}
1B,\\
a,\,\,\,\,{9^8}\\
b,\,\,\,\,{\left( {\dfrac{5}{4}} \right)^3}\\
c,\,\,\,\,{14^4}\\
d,\,\,\,\,\dfrac{{225}}{{343}}\\
2A,\\
a,\,\,\,\,x\\
b,\,\,\,\,3{x^3}\\
c,\,\,\,\,{x^4}\\
d,\,\,\,\,16.{y^4}\\
2B,\\
a,\,\,\,\,x\\
b,\,\,\,\,\dfrac{1}{4}{x^2}\\
c,\,\,\,\,{x^2}\\
d,\,\,\,\, - 7{y^2}
\end{array}\)
Giải thích các bước giải:
Ta có:
\(\begin{array}{l}
1B,\\
a,\\
{9^3}:{9^{ - 5}} = {9^{3 - \left( { - 5} \right)}} = {9^{3 + 5}} = {9^8}\\
b,\\
{\left( {\dfrac{5}{4}} \right)^6}:{\left( {\dfrac{5}{4}} \right)^3} = {\left( {\dfrac{5}{4}} \right)^{6 - 3}} = {\left( {\dfrac{5}{4}} \right)^3}\\
c,\\
{28^4}:{\left( { - 4} \right)^2} = {28^4}:{4^2} = {28^4}:{\left( {{2^2}} \right)^2}\\
= {28^4}:{2^{2.2}} = {28^4}:{2^4} = {\left( {28:2} \right)^4} = {14^4}\\
d,\\
{\left( {\dfrac{9}{7}} \right)^3}:{\left( {\dfrac{9}{5}} \right)^2} = \left( {\dfrac{9}{7}} \right).{\left( {\dfrac{9}{7}} \right)^2}:{\left( {\dfrac{9}{5}} \right)^2}\\
= \dfrac{9}{7}.{\left( {\dfrac{9}{7}:\dfrac{9}{5}} \right)^2} = \dfrac{9}{7}.{\left( {\dfrac{9}{7}.\dfrac{5}{9}} \right)^2} = \dfrac{9}{7}.{\left( {\dfrac{5}{7}} \right)^2}\\
= \dfrac{{{{9.5}^2}}}{{{{7.7}^2}}} = \dfrac{{9.25}}{{7.49}} = \dfrac{{225}}{{343}}\\
2A,\\
a,\\
{x^8}:{x^7} = {x^{8 - 7}} = {x^1} = x\\
b,\\
36{x^7}:12{x^4} = \left( {36:12} \right).\left( {{x^7}:{x^4}} \right) = 3.{x^{7 - 4}} = 3{x^3}\\
c,\\
{\left( { - x} \right)^9}:{\left( { - x} \right)^5} = {\left( { - x} \right)^{9 - 5}} = {\left( { - x} \right)^4} = {x^4}\\
d,\\
32{\left( { - y} \right)^8}:\left( { - 2{y^4}} \right) = 32.{y^8}:2{y^4}\\
= \left( {32:2} \right).\left( {{y^8}:{y^4}} \right) = 16.{y^{8 - 4}} = 16.{y^4}\\
2B,\\
a,\\
{x^3}:{x^2} = {x^{3 - 2}} = {x^1} = x\\
b,\\
2{x^5}:8{x^3} = \left( {2:8} \right).\left( {{x^5}:{x^3}} \right) = \dfrac{1}{4}.{x^{5 - 3}} = \dfrac{1}{4}{x^2}\\
c,\\
{\left( { - x} \right)^5}:{\left( { - x} \right)^3} = {\left( { - x} \right)^{5 - 3}} = {\left( { - x} \right)^2} = {x^2}\\
d,\\
14{\left( { - y} \right)^4}:\left( { - 2{y^2}} \right) = 14{y^4}:\left( { - 2{y^2}} \right)\\
= \left[ {14:\left( { - 2} \right)} \right].\left( {{y^4}:{y^2}} \right) = - 7.{y^{4 - 2}} = - 7{y^2}
\end{array}\)
