Let a, B, C and d be nonnegative integers, then AC + BD + AD + BC = 1997, then a + B + C + D=______ ．

Let a, B, C and d be nonnegative integers, then AC + BD + AD + BC = 1997, then a + B + C + D=______ ．

∵ AC + BD + AD + BC = (AC + AD) + (BD + BC) = a (c + D) + B (c + D) = (a + b) (c + D), 1997 = 1997 × 1, ∵ a, B, C, D are non negative integers, ∵ (a + b) (c + D) = 1997 × 1, ∵ a + B + C + D = 1997 + 1 = 1998

It is known that ABCD = 7, and a, B, C, D are integers a

Because ABCD = 7 and is an integer
Therefore, a, B, C and D can only be selected from - 11 7 - 7
Also a

What's the meaning of ABCD in music?

In each scale on the keys, 1 stands for C, 2 stands for D, 3 stands for e, 4 stands for F, 5 stands for G, 6 stands for a, 7 stands for B
For example, C in C-key means that the stable tone in this mode is C, and then C is regarded as 1 (the first level tone in major) to form the scale 1234567, which is the mode scale of C-key. In C-key music, the music is composed of the seven basic phonemes
In other abdefg tones, the stable tone is abdefg