M=a+b-2√a+8是a+8的算术平方根,所以 a+b-2 = 1,a+b = 3
N=2a-b+4√b-3是 b-3立方根,所以 2a - b + 4 = 1,2a - b = -3
联立,解得 a = 0,b=3
所以 M = √8 = 2√2,N =√b-3 = 0
M + N = √8
所以 M+N平方根 = 4次根号8 或 -4次根号8