Môn Toán Lớp 5: Tính nhanh : A = 2/1×4 + 2/4×7 + 2/7×10 + 2/10×13 + 2/13×16.

2 bình luận về “Môn Toán Lớp 5: Tính nhanh : A = 2/1×4 + 2/4×7 + 2/7×10 + 2/10×13 + 2/13×16.”

1. A=2/(1xx4)+2/(4xx7)+2/(7xx10)+2/(10xx13)+2/(13xx16)

   3/2A = 3/2(2/(1xx4)+2/(4xx7)+2/(7xx10)+2/(10xx13)+2/(13×16))

   3/2A = 3/(1xx4)+3/(4xx7)+3/(7xx10)+3/(10xx13)+3/(13xx16)

   3/2A = 1-1/4+1/4-1/7+1/7-1/10+1/10-1/13+1/13-1/16

   3/2A = 1- 1/16

   3/2A = 16/16-1/16

   3/2A=15/16

   A = 15/16:3/2

   A = 15/16*2/3

   A = 5/8

   Trả lời
2. A = 2/(1xx4) + 2/(4xx7) + 2/(7xx10) + 2/(10xx13) + 2/(13xx16)

   A = ( 1/(1xx4) + 1/(4xx7) + 1/(7xx10) + 1/(10xx13) + 1/(13xx16) ) : 3/2

   A = ( 1/1 – 1/4 + 1/4 – 1/7 + 1/7 -……- 1/16) : 3/2

   A = (1/1 -1/16) : 3/2

   A = 15/16 : 3/2

   A = 5/8

   Trả lời