The double nonnegativity of a quadratic root means that both roots of a quadratic root are nonnegative on the real number axis. Generally speaking, a quadratic radical can be written in the form of AX 2+BX+C (A, B and C are all real numbers), if A >；; 0, b & gt=0, c & gt=0, then this quadratic radical is doubly nonnegative. Double nonnegativity is of great significance to many mathematical problems.