E=1/1.3+1/3.6+1/6.9+.............+1/20.23

<=>E=1/1-1/3+1/3-1/6+1/6-1/9+...........+1/20-1/23

<=>E=1/1-1/23

<=>E=22/23

Kb và k mk nha mn.

Cho hai phan so 1/n va 1/n+1 (n thuoc z)chung to rang h cua hai phan so nay bang hieu cua chung

3.25.8+4.37.6+2.38.12

=24.25+24.37+24.38

=24.(25+37+38)

=24.100

=2400

chúc bạn học tốt :)!

3.25.8+4.37.6+2.38.12 

=24.25+24.37+24.38

=24.(25+37+38)

=24.100=2400

mik nha

3.25.8+4.37.6+2.38.12

= 24 . 25 + 24 . 37 + 24 . 38

= 24( 25 + 37 + 38 )

= 25 .100

= 2500

Ta có : \(\frac{-32}{27}-\left(3x-\frac{7}{9}\right)^3=\) \(\frac{-24}{27}\)

<=> \(-\left(3x-\frac{7}{9}\right)^3=\left(\frac{2}{3}\right)^3\)

<=> \(-\left(3x-\frac{7}{9}\right)=\left(\frac{2}{3}\right)\)

<=> x= \(\frac{1}{27}\) -------chỗ này tắt

\(\dfrac{2^{12}.3^{5}-4^{6}.9^{2}}{(2^{2}.3)^{6}}\)

\(=\dfrac{2^{12}.3^{5}-2^{12}.3^{4}}{2^{12}.3^{6}}\)

\(=\dfrac{2^{12}.3^{4}(3-1)}{2^{12}.3^{4}.3^{2}}\)

\(=\dfrac{2}{9}\)