Đáp án:
$\begin{array}{l}
a) + b)\\
A.B = \dfrac{1}{2}x{y^2}{z^3}t.\dfrac{5}{3}{x^2}y{z^2}{t^3}\\
= \dfrac{5}{6}{x^3}{y^3}{z^5}{t^4}\\
\Leftrightarrow Bậc:15\\
A.C = \dfrac{1}{2}x{y^2}{z^3}t.2{x^2}y{\left( {yz} \right)^2}\\
= x{y^2}{z^3}t.{x^2}y.{y^2}{z^2}\\
= {x^3}{y^5}.{z^5}t\\
\Leftrightarrow Bậc:14\\
A.D = \dfrac{1}{2}x{y^2}{z^3}t.{\left( {\dfrac{1}{2}{x^2}y} \right)^2}.z.{t^3}\\
= \dfrac{1}{2}x{y^2}{z^3}t.\dfrac{1}{4}{x^4}{y^2}.z{t^3}\\
= \dfrac{1}{8}{x^5}{y^4}.{z^4}.{t^4}\\
\Leftrightarrow Bậc:17\\
B.C = \dfrac{5}{3}{x^2}y{z^2}{t^3}.2{x^2}y{\left( {yz} \right)^2}\\
= \dfrac{{10}}{3}{x^4}{y^4}.{z^4}{t^3}\\
\Leftrightarrow Bậc:15\\
B.D = \dfrac{5}{3}{x^2}y{z^2}{t^3}.{\left( {\dfrac{1}{2}{x^2}y} \right)^2}.z.{t^3}\\
= \dfrac{5}{3}{x^2}y{z^2}{t^3}.\dfrac{1}{4}{x^4}{y^2}.z{t^3}\\
= \dfrac{5}{{12}}.{x^6}{y^3}.{z^3}.{t^6}\\
\Leftrightarrow Bậc:18\\
C.D = 2{x^2}y{\left( {yz} \right)^2}.{\left( {\dfrac{1}{2}{x^2}y} \right)^2}.z.{t^3}\\
= 2{x^2}y.{y^2}{z^2}.\dfrac{1}{4}{x^4}{y^2}.z{t^3}\\
= \dfrac{1}{2}{x^6}{y^5}.{z^3}{t^3}\\
\Leftrightarrow Bậc:17
\end{array}$
