Question

tìm x biết:

a)3x chia hết cho x-1

b)2x chia hết cho x+5

Answer 1

a

\(3x⋮x-1\)

\(\Leftrightarrow3\left(x-1\right)+3⋮x-1\)

\(\Leftrightarrow3⋮x-1\)

\(\Leftrightarrow x-1\in\left\{1;3;-1;-3\right\}\)

\(\Leftrightarrow x\in\left\{2;4;-2;0\right\}\)

b

\(2x⋮x+5\)

\(\Leftrightarrow2\left(x+5\right)-10⋮x+5\)

\(\Leftrightarrow10⋮x+5\)

\(\Leftrightarrow x+5\in\left\{1;5;-1;-5;-2;2;10;-10\right\}\)

\(\Leftrightarrow x\in\left\{-4;0;-6;-10;-7;-3;5;-15\right\}\)