Question

Tìm số tự nhiên x, biết:

a)  x chia hết cho 25.

b)  15 chia hết cho x +13

Answer 1

a) ta có: x chia hết cho 25

\(\Rightarrow x\in B_{\left(25\right)}=\left\{25;50;...\right\}\)

b) ta có: 15 chia hết cho x + 13

\(\Rightarrow x+13\inƯ_{\left(15\right)}=\left\{\pm1;\pm3;\pm5;\pm15\right\}\)

nếu x + 13 = 1 => x = -12 (Loại)

..

bn tự xét tiếp nhé

Answer 2

\(a.x⋮25\)

\(\Rightarrow x\in B\left(25\right)\)

\(b.15⋮\left(x+13\right)\)

\(\Rightarrow\left(x+13\right)\in B_{\left(15\right)}=\left\{-15,-5,-3,-1,1,3,5,15\right\}\)

\(x+13=-15\Rightarrow x=-15-13=-28\)

\(x+13=-5\Rightarrow x=-5-13=-18\)

\(x+13=-3\Rightarrow x=-3-13=-16\)

\(x+13=-1\Rightarrow x=-1-13=-14\)

\(x+13=1\Rightarrow x=1-13=-12\)

\(x+13=3\Rightarrow x=3-13=-10\)

\(x+13=5\Rightarrow x=5-13=-8\)

\(x+13=15\Rightarrow x=15-13=2\)

\(x\in\left\{-28;-18;-16;-14;-12;-10;-8;2\right\}\)