Ask some algebra math questions (1) It is known that a = - 2004, B = 2003, C = - 2002, a & sup2; + B & sup2; + C & sup2; + AB + BC AC (2) To find the digit of the product of 2 to the power of 1990 and 3 to the power of 1991 (3) Find X-Y when x + y = 7, X & sup2; + Y & sup2; = 25 (4) Given that a, B, C, D are nonnegative integers, and AC + BD + AD + BC = 199, find a + B + C + D (5) Given a & sup2; - 3A + 1 = 0, find the negative quadratic power of a + 1 / a A & sup2; + A, the quartic power of a + the negative quartic power of A One more question: given X-Y = 5, Y-Z = 4, find X & sup2; + Y & sup2; + Z & sup2; - xy-z & sup2; This problem may be wrong. If not, please solve it

Ask some algebra math questions (1) It is known that a = - 2004, B = 2003, C = - 2002, a & sup2; + B & sup2; + C & sup2; + AB + BC AC (2) To find the digit of the product of 2 to the power of 1990 and 3 to the power of 1991 (3) Find X-Y when x + y = 7, X & sup2; + Y & sup2; = 25 (4) Given that a, B, C, D are nonnegative integers, and AC + BD + AD + BC = 199, find a + B + C + D (5) Given a & sup2; - 3A + 1 = 0, find the negative quadratic power of a + 1 / a A & sup2; + A, the quartic power of a + the negative quartic power of A One more question: given X-Y = 5, Y-Z = 4, find X & sup2; + Y & sup2; + Z & sup2; - xy-z & sup2; This problem may be wrong. If not, please solve it

Original formula = a (a + b) + B (B + C) + C (C-A) = - 2004 * (- 1) + 2003 * 1 + (- 2002) * 2 = 3