Help me :) Hứa cho hay nhất nghen. Bài hơi khó.

`(x - 4) + (x - 6) + (x - 8) + ... + (x - 42) + (x - 44) = 861`

`x - 4 + x - 6 + x - 8 + ... + x - 42 + x - 44 = 861`

`-(4 + 6 + 8+ ... + 42 + 44)  + [(44 - 4) : 2 + 1] x = 861`

`-((4 + 44) [(44 - 4) : 2 + 1])/2 + 21x = 861`

`(-504) + 21x = 861`

`21x = 861 + 504`

`x = 1365 : 21`

`x = 65`

`(5 - x) + (7 - x) + (9 - x) + ... +(95 - x) + (97 - x) = 47.48`

`5 - x + 7 - x + 9 - x + ... + 95 - x + 97 - x = 2256`

`(5 + 7 + 9 + ... + 95 + 97) - [(97 - 5) : 2 + 1] x = 2256`

`((97 + 5)[(97 - 5) : 2 + 1])/2 - 47x = 2256`

`2397 - 47x = 2256`

`47x = 2397 - 2256`

`x = 141 : 47`

`x = 3`

`x + (x - 1) + (x - 2) + (x - 3) + ... + (x - 99) + (x - 100) = 505`

`x + x - 1 + x - 2 + x - 3 + ... + x - 99 + x - 100 = 505`

`-(1+2+3+...+99+100) + [(100 - 1) : 1 + 2] x = 505`

`-((1 + 100) [(100 - 1) : 1 + 1])/2 + 101x = 505`

`(-5050) + 101x = 505`

`101x = 505 + 5050`

`x = 5555 : 101`

`x = 55`

`(x + 5) + (x + 10) + (x + 15) + ... + (x + 55) + (x + 60) = 450`

`x + 5 + x + 10 + x + 15 + ... + x + 55 + x + 60 = 450`

`(5 + 10 + 15 + ... + 55 +60) + [(60 - 5) : 5 + 1]x = 450`

`((5 + 60) [(60-5) : 5 + 1])/2 + 12 x = 450`

`390 + 12 x = 450`

`12x = 450 - 390`

`x = 60 : 12`

`x = 5`

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