b: =>25 chia hết cho x
=>\(x\in\left\{1;-1;5;-5;25;-25\right\}\)
c: =>-15 chia hết cho x
=>\(x\in\left\{1;-1;3;-3;5;-5;15;-15\right\}\)
d: =>6x-3 chia hết cho 4x-7
=>12x-6 chia hết cho 4x-7
=>12x-21+15 chia hết cho 4x-7
=>\(4x-7\in\left\{1;-1;3;-3;5;-5;15;-15\right\}\)
hay \(x\in\left\{2;1;3;-2\right\}\)