504 nha

1x9x8x7=504

k ah nhe!!

Câu trả lời là:

 504

 Đ/s:504

k nha

S=1/4+1/8+1/16+1/32+1/64+1/128

\(S=\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^7}\)

\(2S=2\left(\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^7}\right)\)

\(2S=\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^6}\)

\(2S-S=\left(\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^6}\right)-\left(\frac{1}{2^2}+\frac{1}{2^3}+...+\frac{1}{2^7}\right)\)

\(S=\frac{1}{2}-\frac{1}{2^7}\)

\(\frac{4}{11}< \frac{x}{20}< \frac{5}{11}\Rightarrow\frac{80}{220}< \frac{11.x}{220}< \frac{100}{220}\)

\(\Rightarrow80< 11.x< 100\)

\(\Rightarrow11.x\in\left\{88;99\right\}\)

\(\Rightarrow x\in\left\{8;9\right\}\)

35:5=7. ket qua =7

-32.(-56)+16.88=32.56+16.88

                      =32.56+32.44

                      =32.(56+44)

                      =32.100

                      =3200