\(\dfrac{3.3}{20.23}+\dfrac{3.3}{23.26}+...+\dfrac{3.3}{77.80}\)
\(=3\left(\dfrac{3}{20.23}+\dfrac{3}{23.26}+...+\dfrac{3}{77.80}\right)\)
\(=3\left(\dfrac{1}{20}-\dfrac{1}{23}+\dfrac{1}{23}-\dfrac{1}{26}+...+\dfrac{1}{77}-\dfrac{1}{80}\right)\)
\(=3\left(\dfrac{1}{20}-\dfrac{1}{80}\right)\)
\(=3.\dfrac{3}{80}=\dfrac{9}{80}< 1\left(đpcm\right)\)
Vậy...
Bài 3 : Chứng minh rằng :
\(\dfrac{3^2}{20.23}+\dfrac{3^2}{23.26}+...+\dfrac{3^2}{77.80}< 1\)
Tính tổng:
a) \(\frac{3^2}{20.23}+\frac{3^2}{23.26}+\frac{3^2}{26.29}+...+\frac{3^2}{77.80}\)
Cho A gồm 100 số hạng :\(\dfrac{1}{1.1!}\) + \(\dfrac{1}{2.2!}\) + \(\dfrac{1}{3.3!}\) + ... + \(\dfrac{1}{2013.2013!}\)
Chứng minh rằng : A < \(\dfrac{3}{2}\)
Tính nhanh
a)4^7.3^4.9^6:6^13
b2^3.3^2-5^16:25^7
ai nhanh mk sẽ tick
Tính : \(\frac{25^3.3+25^3.5}{2^{27}}\)
Tính nhanh
1.1!-2.2! + 3.3!+... 9. 9 !
\(\xrightarrow[2^2.3^2.5]{2^3.3^4}\)
Tính giá trị biểu thức
tính
2x-2^3.3^2=138
(6x-3^4).7^3=3.7^4
Thu gọn:
\(A=\dfrac{2^4.3^3+2^3.3^4}{2^5.3^3-2^{\text{ 4}}.3^3}\)
