\(\frac{21^2.14.125}{35^3.6}\)

\(=\frac{7^2.3^2.2.7.5^3}{7^3.5^3.2.3}\)

\(=\frac{7^3.3^2.2.5^3}{7^3.5^3.2.3}\)

\(=3\)

Bo may la binh day k di hieu ashdbfgbgygygggydfsghuyfhdguuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu3

Bo may la binh day k di hieu ashdbfgbgygygggydfsghuyfhdguuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu3

1 đề xi mét khối

Bo may la binh day k di hieu ashdbfgbgygygggydfsghuyfhdguuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu3

abcd=2097

Nhớ k cho mình!!

=a.1000+b.100+c.10+d-(a+b+c+d)

=a.999+a+b.99+b+c+9+c+d-(a+b+c+d)

=a.999+b.99+c.9

mà 999;99;9 đều chia hết 9 nên abcd-(a+b+c+d) chia hết 9

a) A = 1 + 3 + 3² + 3³ + ...+ 3³⁵

=> 3A = 3 + 3² + 3³ + 3⁴ +...+ 3³⁶

=> 3A - A  = 3³⁶ - 1

\(\Rightarrow A=\frac{3^{36}-1}{2}\)

b) ta có: A = 1 + 3 + 3² + 3³ +...+ 3³⁵ ( có 36 số hạng)

A = (1+3) + (3² + 3³) + ...+ (3³⁴ + 3³⁵) ( có 13 nhóm)

A = 4 + 3².(1+3) + ...+ 3³⁴.(1+3)

A = 4 + 3².4 + ...+ 3³⁴.4

A = 4.(1+3² +...+ 3³⁴) chia hết cho 4

..

phần còn lại bn làm tương tự  nha! phần b bn nhóm 3 số hạng lại vs nhau, xog làm như trên là ra !
 

Gọi số đó là abc

Theo bài ra ta có cba-abc=792

(100c+10b+a)-(100a+10b+c)=792

100c+10b+a-100a-10b-c=792

99c-99a=792

99(c-a)=792

c-a=8

mà c:a=3

3a-a=8

2a=8

a=4; c=12(vô lý)

Không có abc

Chứng minh 1994 mũ 100 - 1 và 1994 mũ 100 + 1 không đồng thời là số nguyên tố

ta lấy số dầu cộng số cuối chia khoảng cách cộng 1

 =1018

1-1+1-1+1-1+1-1+1-1+1-1+1-1+1-1+1-1+1-1+1000

= 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 1000 

= 1000

Tâp hợp rỗng {1} {2} {3} {1;2} {1;3} {2;3}

chia ra nha bạn mình ko biết cách trình bày

a .A ko phải là tập hợp con của B vì B ko chứa 5

b. A là tập hợp con của B vì B chứa x,y

c.A là tập con của B vì tận cùng là 0 thì là số chẵn

a) Không

b) Phải

c) Phải