A = - ( 5 - 6 ) - ( 3 - 4 + 5 - 7 )

A = -5 + 6 - 3 + 4 - 5 + 7

A = ( 6 + 4 ) + ( -5 + (-5) ) + ( -3 + 7 )

A = 10 + (-10) + 4

A = 0 + 4

A = 4

P = ( 1 + 3 + 5 + ... + 47 + 49 ) - ( 2 + 4 + 6 + ... + 48 + 50 )

P = \(\frac{\left(1+49\right)\cdot\left(\left(49-1\right):2+1\right)}{2}\)  -  \(\frac{\left(2+50\right)\cdot\left(\left(50-2\right):2+1\right)}{2}\)

P = \(625-650\)

P = \(-25\)

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

  1-2+3-4+5-6+...+47-48+49-50

= (1-2)+(3-4)+(5-6)+...+(47-48)+(49-50) có 25 số hạng

=-1 . 25

=-25

xin like

a.so so hang cua tong do la (49-1)/2+1=25

tong cac so hang do la (49+1)*25/2=625

b. lam tuong tu nhu cau a nha ban

a, Từ 1 đến 49 có:  ( 49 - 1 ) : 2 + 1 = 25 ( số hạng )

 1 + 3 +  5 + 7 + ... + 45 + 47 + 49

= ( 49 + 1 ) x 25 : 2

= 625

đơn giản thôi

\(A=\frac{2}{2\cdot3\cdot4}+\frac{2}{3\cdot4\cdot5}+...+\frac{2}{47\cdot48\cdot49}+\frac{2}{48\cdot49\cdot50}\)

\(A=\frac{1}{2\cdot3}-\frac{1}{3\cdot4}+\frac{1}{3\cdot4}-\frac{1}{4\cdot5}+...+\frac{1}{47\cdot48}-\frac{1}{48\cdot49}+\frac{1}{48\cdot49}-\frac{1}{49\cdot50}\)

\(A=\frac{1}{2\cdot3}-\frac{1}{49\cdot50}\)

\(A=\frac{1}{6}-\frac{1}{2450}\)

\(A=\frac{611}{3675}\)

mong giúp đc bn.thk cho mk 

1+3+5+7+...+47+49+...+(-2)+(-4)+(-6)+...+(-48)+(-50)

=(-2+1)+(-4+3)+...+(-50+49)

=(-1)+(-1)+(-1)+...+(-1) (25 số -1)

= -25