6/7-1/2+2/3

=5/14+2/3

=43/42

14/2:7/9x4/5

=9x4/5

=36/5

6/7 - 1/2 + 2/3 = 43/42

14/2 : 7/9 x 4/5 = 36/5

\(\left(\frac{\sqrt{14}-\sqrt{7}}{1-\sqrt{2}}+\frac{5-\sqrt{5}}{1-\sqrt{5}}\right):\frac{1}{\sqrt{7}-\sqrt{5}}.\)

\(=\left(\frac{\sqrt{7}\left(\sqrt{2}-1\right)}{1-\sqrt{2}}+\frac{\sqrt{5}\left(\sqrt{5}-1\right)}{1-\sqrt{5}}\right):\frac{1}{\sqrt{7}-\sqrt{5}}.\)

\(=\left(\frac{-\sqrt{7}\left(1-\sqrt{2}\right)}{1-\sqrt{2}}+\frac{-\sqrt{5}\left(1-\sqrt{5}\right)}{1-\sqrt{5}}\right):\frac{1}{\sqrt{7}-\sqrt{5}}.\)

\(=\left(\left(-\sqrt{7}\right)+\left(-\sqrt{5}\right)\right)\cdot\frac{\sqrt{7}-\sqrt{7}}{1}\)

\(=-\left(\sqrt{7}+\sqrt{5}\right)\cdot\frac{\sqrt{7}-\sqrt{5}}{1}\)

\(=\frac{-\left(\sqrt{7}+\sqrt{5}\right)\left(\sqrt{7}-\sqrt{5}\right)}{1}\)

\(=\frac{-\left(7-5\right)}{1}=-2\)

1+3+5+.......+35+37+39

=(1+39)+(3+37)+(5+35)+.............+(19+21)

=40+40+............+40(có 10 số 40)

=40 x 10

=400

19x(39+1):2=380

Có số số hạng ở dãy là:

(2017 - 1) : 3 + 1 = 673

Vậy tổng là:
(2017+1) x 673 : 2 = 679 057

vaqy aii ncha biet nnhung phai viet ro ra co nhu the nay nay :(1+2017)+(4+2014+...+bao nhieu so o giua ay minh tinh ko ra

Kết quả k tính đc vì dãy số k có quy luật

ko co quy luat

ai tra loi dung cho h

A = 1 + (-3) +5 + (-7)+............+ 97 + (-99) + 101

A = ( -2 ) + ( - 2 ) +..........+ ( -2 )  + 101         ( có 25 số -2 )

A = -2 . 25 + 101 

A = - 50 + 101

A = 51

\(\frac{1}{42}+\frac{1}{30}+\frac{1}{20}+\frac{1}{12}+\frac{1}{6}+\frac{1}{2}=\frac{1}{1\times2}+\frac{1}{2\times3}+....+\frac{1}{6\times7}=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-...-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\)= 1 - 1/7 = 6/7