Đáp án:
$a)
+) x=2\Rightarrow A=1\\
+) x=-2\Rightarrow A=-15\\
b)B=x^2+xy^5+y^3$
Bậc là 6
c)
$M=x^3-x^2+1+xy^5+y^3$
$M=3$
Giải thích các bước giải:
$a) |x|=2\Leftrightarrow {\left[\begin{aligned}x=2\\x=-2\end{aligned}\right.}\\
+) x=2\Rightarrow A=2^3-2.2^2+1=8-8+1=1\\
+) x=-2\Rightarrow A=(-2)^3-2.(-2)^2+1=-8-8+1=-15\\
b)B=x^2+2xy^5-3x^3+2y^3+3x^3-y^3\\
=x^2+xy^5+(-3x^3+3x^3)+(2y^3-y^3)\\
=x^2+xy^5+y^3$
Bậc là 6
c)
$M=A+B=x^3-2x^2+1+x^2+xy^5+y^3\\
=x^3+(-2x^2+x^2)+1+xy^5+y^3\\
=x^3-x^2+1+xy^5+y^3$
Ta có $2^{x+1}.3^y=12^x$
$\Leftrightarrow 2^{x+1}.3^y=(2^2.3)\\
\Leftrightarrow 2^{x+1}.3^y=2^{2x}.3^x\\
\Leftrightarrow {\left\{\begin{aligned}x+1=2x\\y=x\end{aligned}\right.}\\
\Leftrightarrow {\left\{\begin{aligned}x-2x=-1\\y=x\end{aligned}\right.}\\
\Leftrightarrow {\left\{\begin{aligned}-x=-1\\y=x\end{aligned}\right.}\\
\Leftrightarrow {\left\{\begin{aligned}x=1\\y=1\end{aligned}\right.}\\
\Rightarrow M=1^3-1^2+1+1.1^5+1^3=1-1+1+1+1=3$
