Giải thích các bước giải:

1.Ta có:

$A=5x^2\cdot 2y^2-5\cdot 3xy-x^2y+6x^2y^2$

$\to A=10x^2y^2-15xy-x^2y+6x^2y^2$

$\to A=-x^2y+16x^2y^2-15xy$

$\to A$ có bậc $2+2=4$

2.Ta có:

$B=3x\cdot x^4+4x\cdot x^3-5\cdot x^2\cdot x^3-5x^2\cdot x^2$

$\to B=3x^5+4x^4-5x^5-5x^4$

$\to B=-2x^5-x^4$

$\to B$ có bậc $5$

3.Ta có:

$C=2x^2yz+4xy^2z-5x^2yz+xy^2z$

$\to C=-3x^2yz+5xy^2z$

$\to C$ có bậc $2+1+1=4$

4.Ta có:

$D=5x^3y^2+4x^2y^2-x^3+8x^2y^2-5x^3$

$\to D=5x^3y^2-6x^3+12x^2y^2$

$\to D$ có bậc là $3+2=5$

5.Ta có:

$E=3x^2y-\dfrac14xy+1-3x^2y+\dfrac12xy-\dfrac14$

$\to E=3x^2y-3x^2y+\dfrac12xy-\dfrac14xy+1-\dfrac14$

$\to E=\dfrac14xy+\dfrac34$

$\to E$ có bậc $1+1=2$

6.Ta có:

$F=3x^5-\dfrac12x^2y-\dfrac34xy^2-3x^5-\dfrac34x^2y$

$\to F=-\dfrac{1}{2}x^2y-\dfrac{3}{4}xy^2-\dfrac{3}{4}x^2y$

$\to F=-\dfrac{5}{4}x^2y-\dfrac{3}{4}xy^2$

$\to F$ có bậc $2+1=3$

7.Ta có:

$G=x^3-5xy+3x^3+xy-x^2+\dfrac12xy$

$\to G=4x^3-x^2-\dfrac{7}{2}xy$

$\to G$ có bậc $3$

8.Ta có:

$H=3xy^5-3x^6y^7+\dfrac12x^2y-3xy^5+3x$

$\to H=-3x^6y^7+\dfrac{1}{2}x^2y+3x$

$\to H$ có bậc $6+7=13$