So sánh tổng : S = 1/5 + 1/9 + 1/10 + 1/41 + 1/42 với 1/2

S=

=50/50+50/49+50/48+...+50/2

=50.(1/50+1/49+1/48+...+1/4+1/3+1/2)

=50

P=

P=(1/49+1)+(2/48+1)+...+(48/2+1)+1

P= 50/49+50/48+....+50/2+50/50=1

vậy s/p = 1/50

Ax2=1x2/1x2x3+1x2/2x3x4+...+1x2/48x49x50

Ax2=1/1x2-1/2x3+1/2x3-1/3x4+...+1/48x49-1/49x50

Ax2=1/1x2-1/49x50

Ax2=1/2-1/2450

Ax2=1225/2450-1/2450

Ax2=1224/2450

A=1224/2450:2

A=1224/2450X1/2

A=1224/4900

A=306/1225

Còn câu trả lời nào khác ko zậy !?!

   .....

Đặt 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 = 1.2.3.4 + 2.3.4.(5 - 1) + 3.4.5.(6 - 2) + ... + 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 + ... + 48.49.50.51 - 47.48.49.50

4A = 48.49.50.51

A = 48.49.50.51 : 4

A = 1499400

1.2.3 + 2.3.4 + 3.4.5 + ... + 48.49.50

Đặt 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 = 1.2.3.4 + 2.3.4.(5-1) + 3.4.5.(6-2) + ... + 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 + ... + 48.49.50.51 - 47.48.49.50

    4A = ( 1.2.3.4 + 2.3.4.5 + 3.4.5.6 + ... + 48.49.50.51 ) - ( 1.2.3.4 - 2.3.4.5 - 47.48.49.50 )

    4A = \(\frac{48.49.50.51}{4}\)

      A = 1499400

A = 1 × 2 × 3 + 2 × 3 × 4 + .....+ 48 × 49 × 50

ta có 4 x A = 1 x 2 x 3 x 4 + 2 x 3 x 4 x (5 -1) + .....+ 48 × 49 × 50 x (51 - 47)

= 1 x 2 x 3 x 4 +  2 x 3 x 4 x 5 - 1 x 2 x 3 x 4 + ... + 48 x 49 x 50 x 51 - 47 x 48 x 49 x 50

= 48 x 49 x 50 x 51

suy ra A = (48 x 49 x 50 x 51) : 4

              = 12 x 49 x 50 x 51

nhớ k cho mik nha rùi mik lm nốt cho

P = 1/49+2/48+3/47+...+48/2+49/1

Cộng 1 váo mỗi p/s trong 48 p/s đầu , trừ p/s cuối đi 48 ta đượ

P=(1/49+1)+(2/48+1)+...+(48/2+1)+1

P= 50/49+50/48+....+50/2+50/50

Đưa ps cuối lên đầu

P=50/50+50/49+50/48+...+50/2

=50.(1/50+1/49+1/48+...+1/4+1/3+1/2)

=50.S

VậyS/P=1/50
 

1/50

 chúc bạn học tốt :-)))

SAI CHÍNH TẢ QUÁ NHIỀU