13/14

còn cách làm thì hổng biết

mình có cách làm rồi chờ tí nhé

\(\left(1-\frac{1}{49}\right)\left(1-\frac{1}{64}\right)\left(1-\frac{1}{81}\right)\left(1-\frac{1}{100}\right)\left(1-\frac{1}{21}\right)\left(1-\frac{1}{144}\right)\)

\(=\frac{48}{49}.\frac{63}{64}.\frac{80}{81}.\frac{99}{100}.\frac{120}{121}.\frac{144}{143}\)

\(=\frac{48.63.80.99.120.143}{49.64.81.100.121.144}\)

\(=\frac{6.8.7.9.8.10.11.9.20.6.13.11}{7.7.8.8.9.9.10.10.11.11.6.2.6.2}\)

\(=\frac{13}{14}\)

=(48/49) x (63/64) x (80/81) x (99/100) x (120/121) x (143/144)

=(6x8/7x7) x (7x9/8x8) x (8x10/9x9) x (9x11/10x10) x (10x12/11x11) x (11x13/12x12)

=\(\frac{6x8x8x10x10x12x7x9x9x11x11x13}{7x7x8x8x9x9x10x10x11x11x12x12}\)

rút gọn đi còn: 13/14

a) \(\dfrac{49}{81}=\dfrac{7^x}{9^x}\)(sửa đề)

\(\Leftrightarrow\left(\dfrac{7}{9}\right)^2=\left(\dfrac{7}{9}\right)^x\)\(\Rightarrow x=2\)

b) \(\dfrac{-64}{343}=\left(-\dfrac{4^x}{7^x}\right)\)(sửa đề)

\(\Leftrightarrow\left(-\dfrac{4}{7}\right)^3=\left(-\dfrac{4}{7}\right)^x\) \(\Rightarrow x=3\)

c) \(\dfrac{9}{144}=\dfrac{3^x}{12^x}\)(sửa đề)

\(\Leftrightarrow\left(\dfrac{3}{12}\right)^2=\left(\dfrac{3}{12}\right)^x\Rightarrow x=2\)

d) \(-\dfrac{1}{32}=\left(-\dfrac{1^x}{2^x}\right)\)(sửa đề)

\(\Leftrightarrow\left(-\dfrac{1}{2}\right)^5=\left(-\dfrac{1}{2}\right)^x\Rightarrow x=5\)

Mong bạn xem lại đề bài.

1.3168189e+13

1 x 4 x 9 x 16 x 25 x 36 x 49 x 64 x 81 x 100

\(=1,316818944_{\times10^{13}}\)