tính nhanh
6/9×11+6/11×13+..+6/97×99
2-1/32-1/64–..-1/2048
20062006×200720072007/200620062006×20072007
tính nhanh 6/9×11+6/11×13+..+6/97×99 2-1/32-1/64–..-1/2048 20062006×200720072007/200620062006×20072007
By Aaliyah
By Aaliyah
tính nhanh
6/9×11+6/11×13+..+6/97×99
2-1/32-1/64–..-1/2048
20062006×200720072007/200620062006×20072007
Đáp án:
$\frac{{10}}{{33}}$
Giải thích các bước giải:
$\begin{array}{l}
\frac{6}{{9 \times 11}} + \frac{6}{{11 \times 13}} + … + \frac{6}{{97 \times 99}}\\
= \frac{6}{2} \times \left( {\frac{2}{{9 \times 11}} + \frac{2}{{11 \times 13}} + … + \frac{2}{{97 \times 99}}} \right)\\
= 3 \times \left( {\frac{1}{9} – \frac{1}{{11}} + \frac{1}{{11}} – \frac{1}{{13}} + … + \frac{1}{{97}} – \frac{1}{{99}}} \right)\\
= 3 \times \left( {\frac{1}{9} – \frac{1}{{99}}} \right)\\
= 3 \times \frac{{10}}{{99}} = \frac{{10}}{{33}}
\end{array}$
Giai thích + Trả lời đầy đủ
Ta có :
`=` `6/2 ×` `( 2/{9×11}` `+` `2/{11 × 13}` `+………+` `2/{97 ×99 }`
`=` `3 ×` `(1/9 – 1/11 + 1/11 – 1/13….+1/97 – 1/99)`
`=` `3 × (1/9 – 1/99)`
`=` `3 ×10/99`
`=` `10/33`