\(B=x^5y^2+\dfrac{1}{2}x^5y^2-6xy+1=\dfrac{3}{2}x^5y^2-6xy+1\)
\(B=-\dfrac{1}{7}x^2y+x^5y^2-xy+\dfrac{1}{2}x^5y^2-5xy+\dfrac{1}{7}x^2y+2021^0\\ =\left(-\dfrac{1}{7}x^2y+\dfrac{1}{7}x^2y\right)+\left(x^5y^2+\dfrac{1}{2}x^5y^2\right)-\left(xy+5xy\right)+1\\ =0+\dfrac{3}{2}x^5y^2-6xy+1\\ =\dfrac{3}{2}x^5y^2-6xy+1\)