Tính

a) To solve the equation 7x^2y^2 - 21xy^2 - 7xy = -14xy, we can start by combining like terms:

7x^2y^2 - 21xy^2 - 7xy + 14xy = 0

Simplifying further:

7x^2y^2 - 7xy^2 + 7xy = 0

Factoring out a common factor of 7xy:

7xy(x^2 - y + 1) = 0

Setting each factor equal to zero:

7xy = 0 or x^2 - y + 1 = 0

This gives us two possible solutions:

1) 7xy = 0
This equation is satisfied when either x = 0 or y = 0.

2) x^2 - y + 1 = 0
This equation does not have a simple solution for x and y.

b) To simplify the expression x^3 + 2x^2y - x - 2y, we can combine like terms:

x^3 + 2x^2y - x - 2y

This expression cannot be simplified further.

c) To simplify the expression x^2 - 2xy + y^2 - xz - yz, we can combine like terms:

x^2 - 2xy + y^2 - xz - yz

This expression cannot be simplified further.

d) To simplify the expression x^2 - 2xy + x - 2ty, we can combine like terms:

x^2 - 2xy + x - 2ty

This expression cannot be simplified further.