Given that the number corresponding to point a on the number axis is a, the number corresponding to point B is B, and | a + 4 | + (B-1) 2 (this is the second power) = 0, the distance between a and B is recorded as | ab |, (2) Let the number corresponding to point P on the number axis be X. when PA Pb = 2, find the value of X (3) If the point P is on the left side of a, m and N are the midpoint of PA and Pb respectively, when P moves on the left side of a, the following two conclusions (1) the value of PM + PN remains unchanged; (2) the value of PN - PM remains unchanged. (1) (2) there is only one correct conclusion, judge and find its value

Given that the number corresponding to point a on the number axis is a, the number corresponding to point B is B, and | a + 4 | + (B-1) 2 (this is the second power) = 0, the distance between a and B is recorded as | ab |, (2) Let the number corresponding to point P on the number axis be X. when PA Pb = 2, find the value of X (3) If the point P is on the left side of a, m and N are the midpoint of PA and Pb respectively, when P moves on the left side of a, the following two conclusions (1) the value of PM + PN remains unchanged; (2) the value of PN - PM remains unchanged. (1) (2) there is only one correct conclusion, judge and find its value

1. Because | a + 4 | + (B-1) 2 (this is the second power) = 0, so a = - 4, B = 1
So the length of line ab | ab | = | - 4-1 | = 5
2. Because | PA | - | Pb | = 2, so | x + 4 | - | X-1 | = 2 classification discussion when x > 1, x-4-x + 1 = - 3 is not equal to 2 when - 4