If the value of polynomial 2mx2-x2 + 5x + 8 - (7x2-3y + 5x) is independent of X, the value of M2 - [2M2 - (5m-4) + M] is obtained

If the value of polynomial 2mx2-x2 + 5x + 8 - (7x2-3y + 5x) is independent of X, the value of M2 - [2M2 - (5m-4) + M] is obtained

Since the value of polynomial has nothing to do with X, that is, the coefficients of terms containing X are all zero, then 2mx2-x2 + 5x + 8 - (7x2-3y + 5x) = (2m-8) x2 + 3Y + 8; so 2m-8 = 0, that is, M = 4; substituting M = 4 into M2 - [2M2 - (5m-4) + M], then M2 - [2M2 - (5m-4) + M] = - M2 + 4m-4 = - 16 + 16-4 = - 4