72 : (2 x 4) = 72 : 8 = 9

64 : (8 : 4) = 64 : 2 = 32

64 : 8 + 30 = 8 + 30

= 38

127/128

      \(\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}+\frac{1}{64}+\frac{1}{128}\)

\(=\frac{1x64}{2x64}+\frac{1x32}{4x32}+\frac{1x16}{8x16}+\frac{1x8}{16x8}+\frac{1x4}{32x4}+\frac{1x2}{64x2}+\frac{1}{128}\)

\(=\frac{64}{128}+\frac{32}{128}+\frac{16}{128}+\frac{8}{128}+\frac{4}{128}+\frac{2}{128}+\frac{1}{128}\)

\(=\left(\frac{64}{128}+\frac{1}{128}\right)+\left(\frac{32}{128}+\frac{8}{128}\right)+\left(\frac{16}{128}+\frac{4}{128}\right)\)

\(=\frac{65}{128}+\frac{40}{128}+\frac{20}{128}\)

\(=125\)

nhầm , phải bằng\(\frac{125}{128}\)mới đúng

(cách làm ở dưới)

375 – 10 x 3 = 375 - 30

= 345

64 : 8 + 30 = 8 + 30

= 38

   \(1-\frac{1}{2}-\frac{1}{4}-\frac{1}{8}-\frac{1}{16}-\frac{1}{32}\)\(-\frac{1}{64}\)

\(=1-\frac{32}{64}-\frac{16}{64}-\frac{8}{64}-\frac{4}{64}\)\(-\frac{2}{64}-\frac{1}{64}\)

  \(=1-\left(\frac{32}{64}-\frac{16}{64}-\frac{8}{64}-\frac{4}{64}-\frac{2}{64}-\frac{1}{64}\right)\)

\(=1-\frac{1}{64}\)

\(=\frac{64}{64}-\frac{1}{64}\)

\(=\frac{63}{64}\)

= 1/64 nha

1- 1/2 - 1/4 - 1/8 - 1/16 - 1/32 - 1/64 = 1/64

a: =280+8-241

=288-241

=47

b: =400+400+400=1200

Tận cùng là số 8

1*2*3*4*5*6*7+64:8

=5040+8=

=5048

k nhe!

5048

k nhé

Vậy tích trên được rút gọn :

1 x 2 x 3 x 4 x 5 x 6 x 7 + 64 : 8 )

= 1 x 2 x 3 x 4 x 5 x 6 x 7 + 8

= 2 x 3 x 4 x 5 x 6 x 7 + 8

= 6 x 4 x 5 x 6 x 7 + 8

= 24 x 5 x 6 x 7 + 8

=120 x 6 x 7 +8

=720 x 7 + 8 

=5040 + 8

=5048

\(\sqrt{64}-\sqrt{169}+\sqrt{9}=8-13+3=-2\)

\(4\sqrt{3}+\sqrt{27}-\sqrt{75}=4\sqrt{3}+3-5\sqrt{3}=\sqrt{3}\left(4+3-5\right)=2\sqrt{3}\)