Question

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

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

Answer 1

A=3.(1/1.2+1/2.3+1/3.4+.....+1/399.400)

A=3.(1/1-1/2+1/2-1/3+......+1/399-1/400)

A=3.(1-1/400)

A=3.399/400

A=1197/400

Answer 2

A=3.(1/1.2+1/2.3+1/3.4+.....+1/399.400)

A=3.(1/1-1/2+1/2-1/3+......+1/399-1/400)

A=3.(1-1/400)

A=3.399/400

A=1197/400