a, 4( x - 5) - 7( 5 -x ) + 10 ( 5-x) = -3
=> (-4). (5-x) - 7.(5-x) + 10.(5-x) = -3
=> (5-x) . (-4-7+10)= -3
=> (5-x). (-1) = -3
=> 5-x = 3
=> x = 2
Vậy x = 2
b, 3| x- 3| = 15 - |-9| + 7| -3| - (-24)
=> 3.|x-3| = 15 - 9 + 7.3 + 24
=> 3.|x-3| = 111
=> |x-3| = 37
=> \(\left[ \begin{array}{l}x-3=37\\x-3=-37\end{array} \right.\)
=> \(\left[ \begin{array}{l}x=40\\x=-34\end{array} \right.\)
Vậy x ∈ {-34;40}
c, 6 |x -3| - 9 | x-3| = -21
=> |x-3|. (6-9) = -21
=> |x-3| . (-3) = -21
=> |x-3| = 7
=> \(\left[ \begin{array}{l}x-3=7\\x-3=-7\end{array} \right.\)
=> \(\left[ \begin{array}{l}x=10\\x=-4\end{array} \right.\)
Vậy x ∈ {-4; 10}
