Question

[Đỗ Lê Diệu Quỳnh]

tính bằng cách hợp lí

5/ 2x4 + 5/ 4x6 + 5/ 6x8 +.....+ 5/ 14x16

Answer 1

[Trần Thị Diễm Quỳnh]

A=5/2x(2/2x4+2/4x6+2/6x8+...+2/14x16)

=5/2x(1/2-1/4+1/4-1/6+...+1/14-1/16)

=5/2x(1/2-1/16)

=5/2x(7/16)

=35/32

Answer 2

[Trần Hà Quỳnh Như]

Giải

1/2x4+1/4x6+1/6x8+...+1/96x98+1/98x100

= 1/2 x (1/2 - 1/4 + 1/4 - 1/6 + 1/6-1/8 + ... + 1/98 - 1/100)

= 1/2 x (1/2 - 1/100)

= 1/2 x 98/100

= 98/200

ĐS: 98/200