Câu hỏi của Phạm Minh Anh

Question

Các bạn ghi rõ cách làm nha! Mk đang cần gấp lắm nhank mk tích cho. Cảm ơn

Bài 1: Tính nhanh

A= 3/1*2+3/2*3+3/3*4+...+3/399*400

B= 5/1*2+5/2*3+5/3*4+...+5/399*400

C= 2/5*7+2/7*9+2/9*11+...+2/149*151

D= 3/5*7+3/7*9+3/9*11+...+3/149*151

E=11/1*3+11/3*5+11/5*7+...+11/99*101

Mun Pek · Accepted Answer

Bài 1: Tính nhanh:A = 3/1*2 + 3/2*3 + 3/3*4 + ... + 3/399*400=>3A = 1/1*2 + 1/2*3 + 1/3*4 + ... + 1/399*400    3A = 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/399 - 1/400    3A = 1 - 1/400      3A = 400/400 - 1/400      3A = 399/400        A = 399/400 : 3        A = 399/400 . 1/3        A = 133/400.Có gì ko hiểu bn ib mk nha.^^Câu trả lời: Bài 1: Tính nhanh:A = 3/1*2 + 3/2*3 + 3/3*4 + ... + 3/399*400=>3A = 1/1*2 + 1/2*3 + 1/3*4 + ... + 1/399*400    3A = 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/399 - 1/400    3A = 1 - 1/400      3A = 400/400 - 1/400      3A = 399/400        A = 399/400 : 3        A = 399/400 . 1/3        A = 133/400.Có gì ko hiểu bn ib mk nha.^^

Nguyễn Thanh Hiền · Answer

$A=\frac{3}{1.2}+\frac{3}{2.3}+\frac{3}{3.4}+...+\frac{3}{399.400}$$A=3.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{399.400}\right)$$A=3.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{399}-\frac{1}{400}\right)$$A=3.\left(1-\frac{1}{400}\right)$$A=3.\frac{399}{400}$$A=\frac{1197}{400}$$B=\frac{5}{1.2}+\frac{5}{2.3}+\frac{5}{3.4}+...+\frac{5}{399.400}$$B=5.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{399.400}\right)$$B=5.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{399}-\frac{1}{400}\right)$$B=5.\left(1-\frac{1}{400}\right)$$B=5.\frac{399}{400}$$B=\frac{399}{80}$$C=\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}+...+\frac{2}{149.151}$$C=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+...+\frac{1}{149}-\frac{1}{151}$$C=\frac{1}{5}-\frac{1}{151}$$C=\frac{146}{755}$$D=\frac{3}{5.7}+\frac{3}{7.9}+\frac{3}{9.11}+...+\frac{3}{149.151}$$D=\frac{3}{2}.\left(\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}+...+\frac{2}{149.151}\right)$$D=\frac{3}{2}.\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+...+\frac{1}{149}-\frac{1}{151}\right)$$D=\frac{3}{2}.\left(\frac{1}{5}-\frac{1}{151}\right)$$D=\frac{3}{2}.\frac{146}{755}$$D=\frac{219}{755}$$E=\frac{11}{1.3}+\frac{11}{3.5}+\frac{11}{5.7}+...+\frac{11}{99.101}$$E=\frac{11}{2}.\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{99.101}\right)$$E=\frac{11}{2}.\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{99}-\frac{1}{101}\right)$$E=\frac{11}{2}.\left(1-\frac{1}{101}\right)$$E=\frac{11}{2}.\frac{100}{101}$$E=\frac{550}{101}$_Chúc bạn học tốt_Câu trả lời: $A=\frac{3}{1.2}+\frac{3}{2.3}+\frac{3}{3.4}+...+\frac{3}{399.400}$$A=3.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{399.400}\right)$$A=3.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{399}-\frac{1}{400}\right)$$A=3.\left(1-\frac{1}{400}\right)$$A=3.\frac{399}{400}$$A=\frac{1197}{400}$$B=\frac{5}{1.2}+\frac{5}{2.3}+\frac{5}{3.4}+...+\frac{5}{399.400}$$B=5.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{399.400}\right)$$B=5.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{399}-\frac{1}{400}\right)$$B=5.\left(1-\frac{1}{400}\right)$$B=5.\frac{399}{400}$$B=\frac{399}{80}$$C=\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}+...+\frac{2}{149.151}$$C=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+...+\frac{1}{149}-\frac{1}{151}$$C=\frac{1}{5}-\frac{1}{151}$$C=\frac{146}{755}$$D=\frac{3}{5.7}+\frac{3}{7.9}+\frac{3}{9.11}+...+\frac{3}{149.151}$$D=\frac{3}{2}.\left(\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}+...+\frac{2}{149.151}\right)$$D=\frac{3}{2}.\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+...+\frac{1}{149}-\frac{1}{151}\right)$$D=\frac{3}{2}.\left(\frac{1}{5}-\frac{1}{151}\right)$$D=\frac{3}{2}.\frac{146}{755}$$D=\frac{219}{755}$$E=\frac{11}{1.3}+\frac{11}{3.5}+\frac{11}{5.7}+...+\frac{11}{99.101}$$E=\frac{11}{2}.\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{99.101}\right)$$E=\frac{11}{2}.\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{99}-\frac{1}{101}\right)$$E=\frac{11}{2}.\left(1-\frac{1}{101}\right)$$E=\frac{11}{2}.\frac{100}{101}$$E=\frac{550}{101}$_Chúc bạn học tốt_

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