Question

Bài 3 : Tìm số x \(\in\)Z biết :

g, ( x - 6 )\(^2\)= 9                           h, 21\(⋮\)(2x + 5 )                      i, |x| = 3

Answer 1

a.

\(\left(x-6\right)^2=9\)

\(\left(x-6\right)^2=\left(\pm3\right)^2\)

\(x-6=\pm3\)

TH1:

\(x-6=3\)

\(x=3+6\)

\(x=9\)

TH2:

\(x-6=-3\)

\(x=-3+6\)

\(x=3\)

Vậy x = 9 hoặc x = 3.

h.

\(21⋮2x+5\)

=> \(2x+5\inƯ\left(21\right)\)

=> \(2x+5\in\left\{-21;-7;-3;-1;1;3;7;21\right\}\)

=> \(2x\in\left\{-17;-2;2;4;6;8;12;27\right\}\)

=> x \(\in\left\{-\frac{17}{2};-1;1;2;3;4;6;\frac{27}{2}\right\}\)

\(x\in Z\)

=> \(x\in\left\{-1;1;2;3;4;6\right\}\)

i.

\(\left|x\right|=3\)

\(x=\pm3\)

Vậy x = 3 hoặc x = -3