= 243 x 2 + 5 x 243 + 243 x 2 x 2 - 473

= 243 x (2+5+2x2) - 473

= 243 x 28 - 473 

= 6084 - 473

= 6331

   = 243 * (2+5+4) -473

=243 * 10 - 230

=2430 -230

=2200

a) 68 + 95 + 32 + 5 = (68 + 32) + (95 + 5) = 100 + 100 = 200

b) 102 + 7 + 243 + 98 = (102 + 98) + (7 + 243) = 200 + 250 = 450

a 68 + 95 + 32 + 5

=( 68 + 32 ) + ( 95 + 5 )

243x2+5x243+486x2-243

= 243 x2+5x243+486x2-243x1

= 243x ( 2+5+486 x 2 + 1 )

= 243 x          980

= 238140

243x2+5x243+486x2-243

=2x243+5x243+2x2x243-243

=7x243+4x243-1x243

=11x243-1x243

=10x243=2430

(\(\dfrac{2}{3}\) + \(\dfrac{8}{9}\) + \(\dfrac{26}{27}\) + \(\dfrac{80}{81}\) + \(\dfrac{242}{243}\)) : y = 5

Đăt      A = \(\dfrac{2}{3}\) + \(\dfrac{8}{9}\) + \(\dfrac{26}{27}\) + \(\dfrac{80}{81}\) + \(\dfrac{242}{243}\) 

          3A =  2 + \(\dfrac{8}{3}\) + \(\dfrac{26}{9}\) + \(\dfrac{80}{27}\) + \(\dfrac{242}{81}\) 

      3A - A = 2 + \(\dfrac{8}{3}\) + \(\dfrac{26}{9}\) + \(\dfrac{80}{27}\) + \(\dfrac{242}{81}\) - \(\dfrac{2}{3}\)-\(\dfrac{8}{9}\)-\(\dfrac{26}{27}\)-\(\dfrac{80}{81}\)-\(\dfrac{242}{243}\)

       A x (3 - 1) = 2 - \(\dfrac{242}{243}\)+ (\(\dfrac{8}{3}\) - \(\dfrac{2}{3}\))+(\(\dfrac{26}{9}\) - \(\dfrac{8}{9}\))+(\(\dfrac{80}{27}\)-\(\dfrac{26}{27}\))+(\(\dfrac{242}{81}\)-\(\dfrac{80}{81}\))-\(\dfrac{242}{243}\)

      A x 2 = 2 - \(\dfrac{242}{243}\) + 2 + 2 + 2 + 2

     A  x 2 = (2 + 2 + 2  +2 + 2) - \(\dfrac{242}{243}\)

    A  x 2 =  2x5 - \(\dfrac{242}{243}\)

   A  x 2 = 10 - \(\dfrac{242}{243}\)

   A x 2 = \(\dfrac{2188}{243}\)

   A = \(\dfrac{2188}{243}\) : 2

A = \(\dfrac{1094}{243}\)

\(\dfrac{1094}{243}\) : y = 5

  y = \(\dfrac{1094}{243}\) : 5

  y =  \(\dfrac{1094}{1215}\)

3 ; 9 ; 27 ; ..81.. ; 243

tk mình nha!

3;9;27;  81  ;243

số cần điền là 9 vì 3 x 9 = 27, 27 x 9 = 243

3 ; 9 ; 27 ; 9 ; 243

\(A=\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}+\frac{1}{243}+\frac{1}{729}\)

\(3\times A=1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}+\frac{1}{243}\)

\(3\times A-A=\left(1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}+\frac{1}{243}\right)-\left(\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}+\frac{1}{243}+\frac{1}{729}\right)\)

\(2\times A=1-\frac{1}{729}=\frac{728}{729}\)

\(A=\frac{364}{729}\)

243 x 2 + 4 x 243 + 486 x 2 

= 486 + 972 + 972

= 1458 + 972

= 2430

Tính nhanh chứ gì?

486 : 2 = 243 (2 lần 243 là 486 vậy nên chúng có 2 x 2 = 4 lần)

Vì ta phát hiện các chữ số đó đều có 243 và một số số khác nên ta có: 243 x (2 + 4 + 4) = 243 x 10 = 2430

243x2 + 4x243 + 486x2

=243x2 + 4x243 + 243x2x2

=243x2 + 4x243 + 243x4

=243 x(2+4+4)

=243 x 10

= 2430

k mk nha ^_^

1+ 1 /3+1/9+1/27+1/81+1/243+1/729.
Đặt:
S = 1 + 1/3 + 1/9 + 1/27 + 1/81 + 1/243 
Nhân S với 3 ta có:
S x 3 = 3 +1+ 1/3 + 1/9 + 1/27 + 1/81
Vậy: 
S x 3 - S = 3 - 1/243
2S = 728/243
S = 364/243

tick đúng nha

=364/243

đà đà na đa