Tính nha, mik ghi thiếu

Tham khảo link :

https://h.o.c24.vn/hoi-dap/question/208531.html

~Std well~

#Thạc_Trân

Tham khảo nek:

Câu hỏi của Trịnh Mai Yến - Toán lớp 6 | Học trực tuyến - H.vn

Nếu ko coppy thì vô tcn coppy cũng được ko được đánh mạng nhé :>

\(A=1.2.3+2.3.4+3.4.5+...+48.49.50\)

\(4A=1.2.3.4+2.3.4.4+3.4.5.4+...+48.49.50.4\)

\(4A=1.2.3.\left(4-0\right)+2.3.4.\left(5-1\right)+...+48.49.50.\left(51-47\right)\)

\(4A=1.2.3.4-0.1.2.3+2.3.4.5-1.2.3.4+...+48.49.50.51-48.48.49.50\)

\(4A=48.49.50.51\)

\(A=\dfrac{48.49.50.51}{4}=1499400\)

A=1499400 nhe ban !

4A=4.[1.2.3 + 2.3.4 + 3.4.5 + 4.5.6 + . . . . . . + 48.49.50]
4A=1.2.3.4 +2.3.4.4 +3.4.5.4 +4.5.6.4 +.........+48.49.50.4
4A=1.2.3.4 +2.3.4.(5-1) + 3.4.5.(6-2) +4.5.6(7-3)+....+ 48.49.50(51-47)
4A=1.2.3.4 +2.3.4.5 --1.2.3.4 + 3.4.5.6--2.3.4.5 + 4.5.6.7-3.4.5.6+....+ 48.49.50.51--47.48.49.50
4A =48.49.50.51
A=(48.49.50.51)/4

4A=4.[1.2.3 + 2.3.4 + 3.4.5 + 4.5.6 + . . . . . . + 48.49.50] 
4A=1.2.3.4 +2.3.4.4 +3.4.5.4 +4.5.6.4 +.........+48.49.50.4 
4A=1.2.3.4 +2.3.4.(5-1) + 3.4.5.(6-2) +4.5.6(7-3)+....+ 48.49.50(51-47) 
4A=1.2.3.4 +2.3.4.5 --1.2.3.4 + 3.4.5.6--2.3.4.5 + 4.5.6.7-3.4.5.6+....+ 48.49.50.51--47.48.49.50 
4A =48.49.50.51 
A=(48.49.50.51)/4 

đáp số bài này là 1.499.400

4F=4.[1.2.3 + 2.3.4 + 3.4.5 + 4.5.6 + . . . . . . + 48.49.50] 
4F=1.2.3.4 +2.3.4.4 +3.4.5.4 +4.5.6.4 +.........+48.49.50.4 
4F=1.2.3.4 +2.3.4.(5-1) + 3.4.5.(6-2) +4.5.6(7-3)+....+ 48.49.50(51-47) 
4F=1.2.3.4 +2.3.4.5 --1.2.3.4 + 3.4.5.6--2.3.4.5 + 4.5.6.7-3.4.5.6+....+ 48.49.50.51--47.48.49.50 
4F =48.49.50.51 
F=(48.49.50.51)/4 

\(\dfrac{1}{1\cdot2\cdot3}+\dfrac{1}{2\cdot3\cdot4}+...+\dfrac{1}{48\cdot49\cdot50}\)

\(=\dfrac{1}{2}\cdot\left(\dfrac{1}{1\cdot2}-\dfrac{1}{2\cdot3}+\dfrac{1}{2\cdot3}-...+\dfrac{1}{48\cdot49}-\dfrac{1}{49\cdot50}\right)\)

\(=\dfrac{1}{2}\cdot\left(\dfrac{1}{1\cdot2}-\dfrac{1}{49\cdot50}\right)\)

\(=\dfrac{1}{2}\cdot\left(\dfrac{1}{2}-\dfrac{1}{2450}\right)\)

\(=\dfrac{1}{2}\cdot\dfrac{612}{1225}\)

\(=\dfrac{306}{1225}\)

1.2.3+2.3.4+...+48.49.50

=1.50

=50