*Tips:*(1) The equation must have one constant (without

*x*and

*y*).

(2)

*and*

**X***cannot have constant, but can have the variables (for example*

**Y***x*and

*y*).

(3)

**and**

*m***can only have the constant (for example**

*c**a*and

*b*), cannot have the variables

*x*and

*y*.

__Examples__

__(1)__

*X*and*Y*cannot have constant, but can have the variables (for example*x*and*y*)

(2)

(2)

*m*and*c*can only have the constant (for example*a*and*b*), cannot have the variables*x*and*y*