A polynomial Plus + x2y-3xy2 gives the third power of x-3x2y. This polynomial is

A polynomial Plus + x2y-3xy2 gives the third power of x-3x2y. This polynomial is

x^3-3x2y-(x2y-3xy^2)
=x^3-3x2y-x2y+3xy^2
=x^3-4x2y+3xy^2

4. If the polynomial (a + 1) x4y-xby2 + 3x2y-2xy + 1 is a quartic polynomial about X and y, then a + B = (write the process clearly)
I'll give you another 15 points if it's right,

a+1=0
b+2=4
a=-1
b=2
a+b=-1+2=1
explain:
(a + 1) x4y is of degree 5. To be a polynomial of degree 4, it must be a + 1 = 0
The last three terms are up to degree 3. To be a polynomial of degree 4, xby2 must be degree 4, that is, B + 2 = 4