1/2.1/3+1/3.1/4+1/4.1/5+1/5.1/6

=1/2.3+1/3.4+1/4.5+1/5.6

=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6

=1/2-1/6

=2/6=1/3

bangwf 02992830403

\(D=5x^2y+\frac{1}{2}x\)là đa thức nhé . Nên mình chỉ làm A + B thôi

\(A=\frac{1}{2}x^2y\cdot3\left(y^2z\right)^3=\left(\frac{1}{2}\cdot3\right)x^2\left(yy^6\right)z^3=\frac{3}{2}x^2y^7z^3=\frac{3}{2}x^2z^3y^7\)

\(B=-3xz^3\cdot\frac{1}{3}xy^7=\left(-3\cdot\frac{1}{3}\right)\left(xx\right)z^3y^7=-1x^2z^3y^7\)

Tổng của hai đơn thức trên là :

\(A+B=\frac{3}{2}x^2z^3y^7+\left(-1\right)x^2z^3y^7=\left(\frac{3}{2}+\left(-1\right)\right)x^2z^3y^7=\frac{1}{2}x^2z^3y^7\)

\(A=-\dfrac{1}{2.3}-\dfrac{1}{3.4}-\dfrac{1}{4.5}-...-\dfrac{1}{9.10}\)

\(\Rightarrow-A=\dfrac{3-2}{2.3}+\dfrac{4-3}{3.4}+\dfrac{5-4}{4.5}+...+\dfrac{10-9}{9.10}=\)

\(=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{9}-\dfrac{1}{10}=\)

\(=\dfrac{1}{2}-\dfrac{1}{10}=\dfrac{2}{5}\Rightarrow A=-\dfrac{2}{5}\)

giúp mik nha!!!

\(=\dfrac{1}{99}-\dfrac{1}{2}\cdot\left(\dfrac{2}{1\cdot3}+\dfrac{2}{3\cdot5}+...+\dfrac{2}{97\cdot99}\right)\)

=1/99-1/2(1-1/3+1/3-1/5+...+1/97-1/99)

=1/99-1/2*98/99

=1/99-49/99

=-48/99=-16/33

A=-(1/1.3+1/3.5+1/5.7+...+1/97.99)

A=-1/2.(2/1.3+2/3.5+2/5.7+...+2/97.99)

A=-1/2.(1-1/3+1/3-1/5+...+1/97-1/99)

A=-1/2.(1-1/99)=-1/2.98/99

A=(tự bấm máy tính nha)

lam j co tru o dang trc 1/99*97 sai tram trong

đùa nhau à!

\(A=\frac{61}{168}\)