5/15.16+5/16.17+5/17.18+5/18.19+5/19.20

=5(1/15-1/16+1/16-1/17+..+1/19-1/20) 

=5.(1/15-1/20)

=5.1/60

=1/12

\(\frac{5}{15.16}+\frac{5}{16.17}+\frac{5}{17.18}+\frac{5}{18.19}+\frac{5}{19.20}\)

= \(5.\left(\frac{1}{15.16}+\frac{1}{16.17}+\frac{1}{17.18}+\frac{1}{18.19}+\frac{1}{19.20}\right)\)

= \(5.\left(\frac{1}{15}-\frac{1}{16}+\frac{1}{16}-\frac{1}{17}+\frac{1}{17}-\frac{1}{18}+\frac{1}{18}-\frac{1}{19}+\frac{1}{19}-\frac{1}{20}\right)\)

= \(5.\left(\frac{1}{15}-\frac{1}{20}\right)\)

= \(5.\frac{1}{60}\)

= \(\frac{1}{12}\)

\(\frac{5}{15.16}+\frac{5}{16.17}+\frac{5}{17.18}+\frac{5}{18.19}+\frac{5}{19.20}\)

\(=5\left(\frac{1}{15.16}+\frac{1}{16.17}+...+\frac{1}{19.20}\right)\)

\(=5\left(\frac{1}{15}-\frac{1}{16}+\frac{1}{16}-\frac{1}{17}+...+\frac{1}{19}-\frac{1}{20}\right)\)

\(=5\left(\frac{1}{15}-\frac{1}{20}\right)\)

\(=5.\frac{1}{60}\)

\(=\frac{1}{12}\)

Phúc nè tui hỏi chơi thui đc ko? Nhưng mà tui Cần nó để làm một số chuyện

a'15.16.17-14.15.16+16.17.18-....-28.29.30

=>4A=28.29.30-14.15.16=21000=>a=7000

bc,làm tương tự

a.(a+1)=a(a+1)(a+2)---(a-1)a(a+1)

Barack mới tự học toán 6 hơn 1 tuần, có cách giải này

= 10² + 10 + 11² + 11 + 12² + 12 + 13² + 13 + 14² + 14 + 15² + 15 +16² +16 +17² +17 + 18² + 18 + 19² +19 

= 10² + 11² + 13² + 14² + 15² + 16² + 17² + 18² +19² + 10 + 11 +12 +13 + 14 + 15 + 16 +17 + 18 + 19

Lớp 6 gì xương thế

140.28

bạn giải ra đi

3s1=(2.3+3.4+4.5+5.6+...+15.16+16.17).3

3s1=2.3.3+3.4.3+4.5.3+5.6.3+....+15.16.3+16.17.3

3s1=2.3(4-1)+3.4(5-2)+4.5(6-3)+5.6(7-4)+...+15.16(17-14)+16.17(18-15)

3s1=2.3.4-1.2.3+3.4.5-2.3.4+4.5.6-3.4.5+...+15.16.17-14.15.16+16.17.18-15.16.17

3s1=(16.17.18-1.2.3)/3

s1=1630

Bạn chỉ cần : 

tính nhanh 

A =1990² -1992.1998

B=2001² -2000.2002

C =2009²-2007.2011

D= (37.13-13):(24+37.12)

E = (16.17-5) :(16.16+11)

F= (45.16-17):(28+45.15)

ban phai chuyen ra thanh so tu nhien thi moi lam duoc.

E =16(16+1) -5 phan 16.16+11 =16.16+16 - 5phan 16.16 +11 = 16.16 +11 phan 16.16 =11

Trả lời : 

Tôi nghĩ chúng ta phải bảo vệ sức khỏe để phòng ngừa bệnh cúm . giữ sức khỏe chúng ta có cách là chăm sóc tốt bản thân mình , giấc ngủ và chất dinh dưỡng cũng ngăn cản được lạnh của cúm .

hok tốt

tiếng anh nhé

Some remedies to prevent the flu essay (Một vài biện pháp để phòng tránh bệnh cúm bằng tiếng anh

I think we need to stay healthy to prevent the flu, keep as healthy as i can by taking good care of myself. Sleep and nutritional considerations are help to prevent the onset of a cold or flu, a healthy lifestyle helps my immune system to be in its best possible shape, giving me the best chance of being able to fight off the onset of a cold or flu.

I need to eat healthily. Healthy foods such as vegetables, fruit, grains, etc., are an important part of keeping my body nutrition at its optimum. Processing fatty and sugary foods don't give the immune-boosting protection that healthier food does. Sugary foods can decrease immune function.

Exercise regularly. Exercise has enhancing immune-system that can help ward off illness. Overdo too much strenuous or excessive can leave me prone to illness, too. I make sure to get adequate sleep every night, get at least seven to eight hours sleep nightly

          I need to reduce my stress too. Stress can harm the ability of my immune system to work optimally, and people who are stressed tend to catch colds more than less stressed people. Manage my stress is contributing to prevent the flu. Beside, Drinking water may also help wash cold and flu viruses from my throat to my stomach where they cannot survive. Although getting cold doesn't actually cause a cold or flu (the viruses do), but being cold can reduce my stamina and make me feel miserable and fatigued, so i need to stay warm.

In addition, i eat more fruits to get vitamin C that might help me prevent the common cold, and i will also drink more milk, this will be help me healthy and stronger to prevent the cold

bằng 1184

TL
999+185

=1184

HT

999 + 185= 1184

HT