\(21\cdot35\cdot3\cdot25\cdot7\)

\(=21\cdot3\cdot7\cdot35\cdot25\)

\(=21(3\cdot7)\cdot35\cdot25\)

\(=21\cdot21\cdot35\cdot25\)

\(=21^2\cdot875=385875\)

Nghĩ sao không có số nào tròn để tính hợp lí -_-

\(\frac{254+399.253}{254.399-145}=\frac{254+399.253}{\left(253+1\right).399-145}=\frac{254+399.253}{253.399+\left(399-145\right)}\)

\(=\frac{399.253+254}{399.353+354}=1\)

-1911-(1234-1911)

-1911-1234+1911

(-1911+1911)-1234

0 - 1234

-1234

= -1911-1234+1911

=(-1911+1911)-1234

=0-1234

=-1234

âm 1234 đó

895,72+402,68-634,87

=1298,4-634,87

=663,53

895,72 + 402,68 - 634,87 =

= 1298,4 - 634,87

=663,53

tk nha

{ x  (-  N  | x > 3 } 

\(A=\left\{x\inℕ^∗|x-1⋮3\right\}\)

37 + 198 = (37 - 2) + (198 + 2) = 35 + 200 = 235

37 + 198 = 37 + 63 + 35 + 100

             = 100 + 100 +35

             = 200 + 35

             = 235    

37 + 198 = 37+ 63 + 35 + 100

              = 100 + 100 + 35

              = 200 + 35

              = 235  

4x51x7+2x86x7+12x2x7=

(4 x7)x51+(2x7)x86+(2x7)x12=

28x51+14x86+14x12=

14x2x51+14x86+14 x12=

14x102+14x86+14x12=

14x(102+86+12)=

14x200=

2800

4x51x7+2x86x7+12x2x7

(4 x7)x51+(2x7)x86+(2x7)x12

28x51+14x86+14x12

14x2x51+14x86+14 x12

14x102+14x86+14x12

14x(102+86+12)

14x200

2800

=4x51x7+2x86x7+12x2x7

=(4 x7)x51+(2x7)x86+(2x7)x12

=28x51+14x86+14x12

=14x2x51+14x86+14 x12

=14x102+14x86+14x12

=14x(102+86+12)

=14x200

2800

\(-1+6+\left(-11\right)+16+....+996+\left(-1001\right)\)

\(=5+5+....+5+5\)

\(=5.10\)

\(=50\)

-1+6+(-11)+16+.....+996+(-1001)

=[-1+6]+[-11+16]+....+[-991+996]+(-1001)

=5       +      5      +...+       5         + (-1001)

    có 100 số 5

=5 x100+(-1001)

=500+(-1001)

=-501

k cho minh nha

chúc bạn học giỏi

=( 7*5*39)/(13*14*15)

=(7*5*3*13)/(13*7*2*5*3)

=1/2

 \(\frac{7}{13}x\frac{5}{14}x\frac{39}{15}\)

\(=\frac{7x5x39}{13x14x15}\)

\(=\frac{7x5x13x3}{13x7x2x5x3}\)

\(=\frac{1}{2}\)