If a + B = C, a > C, then () A. B must be negative, B. a must be less than B, C. A must be negative, D. must be less than a

If a + B = C, a > C, then () A. B must be negative, B. a must be less than B, C. A must be negative, D. must be less than a

If a + B = C,
B = c-a. because a > C, B = c-a

If the negative number ABC satisfies a + B + C = - 1, then the maximum value of 1 / A + 1 / B + 1 / C is?
It seems very simple, but I just can't do it. I feel a little inferior
Using mean inequality to solve the problem

Encounter this kind of complete symmetry problem, you make each thing equal commonly, can come to an extremum

The nonnegative number A.B.C satisfies a + B + C = 30, 3A + B-C = 50. Find the maximum and minimum of n = 5A + 4B + 2C

3A + 3B + 3C = 90, 3A + B-C = 50, 6a + 4B + 2C = 140, so n = 140-a from a + B + C = 30, 3A + B-C = 50, B = 40-2a, C = A-10, because non negative numbers a, B, C, so 40-2a ≥ 0, a ≤ 20, A-10 ≥ 0, a ≥ 10, so 10 ≤ a ≤ 20-20 ≤ - a ≤ - 10, so 120 ≤ n ≤ 130, the maximum and minimum of N are obtained