a. 

1+2+3+...+99+100

=(1+100)*100/2

=5050

b.12+14+16+...+38

=(12+38)*[(38-12)/2+1]/2

=350

a) 1 + 2 + 3 +... + 99 + 100 

= \(\left[\left(100-1\right):1+1\right]\times\frac{100+1}{2}\)

= \(100\times\frac{101}{2}\)

= \(5050\)

b) 12 +14 + 16 + ... + 36 + 38

= \(\left[\left(38-12\right):2+1\right]\times\frac{38+12}{2}\)

=\(14\times25\)

= \(350\)

\((\frac{1}{2}+\frac{1}{4}+\frac{1}{6}) \)x \((\frac{36}{9}-\frac{12}{9}:\frac{1}{3}) \)

\(= (\frac{1}{2}+\frac{1}{4}+\frac{1}{6}) \) x \((\frac{36}{9}-\frac{36}{9})\)

\( = (\frac{1}{2}+\frac{1}{4}+\frac{1}{6}) \) x \(0\)

\(= 0\)

Ai trả lời đc mình sẽ 👍 nha 

a. 9/7 < 11/13

b. 12/17 > 5/36

a. 9/7 < 11/13

b. 12/17 > 5/36

hợp lí á bạn

   \(\dfrac{3}{8}+\dfrac{9}{2}\times\dfrac{12}{16}-\dfrac{9}{4}:3\)

= \(\dfrac{3}{4}\times\dfrac{1}{2}+\dfrac{9}{2}\times\dfrac{3}{4}-\dfrac{3}{4}\times3:3\)

= \(\dfrac{3}{4}\times\dfrac{1}{2}+\dfrac{9}{2}\times\dfrac{3}{4}-\dfrac{3}{4}\times1\)

= \(\dfrac{3}{4}\times\left(\dfrac{1}{2}+\dfrac{9}{2}-1\right)\)

= \(\dfrac{3}{4}\times\left(5-1\right)\)

= \(\dfrac{3}{4}\times4\)

= 3

A = (2 + 2²) + (2³ + 2⁴ ) +…(2¹⁹⁹ + 2²⁰⁰)

A = 6 + 2² (2 + 2² ) +… + 2¹⁹⁸ (2 + 2²)

A = 6 + 2² (6 ) +… + 2¹⁹⁸ (6)

A = 6(1 + 2² +… + 2¹⁹⁸)

Vậy A chia hết cho 6

a) \(\left(\frac{2}{7}+\frac{3}{8}+\frac{12}{7}+\frac{5}{8}\right).\frac{19}{36}\)

\(=\left\{\left(\frac{2}{7}+\frac{12}{7}\right)+\left(\frac{3}{8}+\frac{5}{8}\right)\right\}.\frac{19}{36}\)

\(=\left(\frac{14}{7}+\frac{8}{8}\right).\frac{19}{36}\)

\(=\left(2+1\right).\frac{19}{36}\)

\(3.\frac{19}{36}=\frac{19}{12}\)

hummumumumhuhuhu=(

a: \(=\dfrac{4}{3}\cdot\dfrac{32}{10}+\dfrac{8}{3}\cdot\dfrac{36}{10}-\dfrac{4}{10}\cdot\dfrac{12}{9}\)

\(=\dfrac{128}{30}+\dfrac{288}{30}-\dfrac{48}{90}=\dfrac{416}{30}-\dfrac{24}{30}=\dfrac{392}{30}=\dfrac{196}{15}\)

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20

=(1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)+20+10

=20+20+20+20+20+20+20+20+20+20+10

=20×10+10

=200+10

=210

= ( 1 + 19 ) + ( 2 + 18 ) + ( 3 + 17 ) + (4 + 16 ) + ( 5 + 15 ) + ( 6 + 14 ) + ( 7 + 13 ) + ( 8 + 12) + ( 9+ 11 ) + 20

= 20 + 20 + 20 +20 +  20 +20 + 20 + 20 + 20 +20

= 20 x 10

= 200

tui đầu tiên đó 

a) 36 + 12 + 14 + 38 = (36 + 14) + (12 + 38)

                                 = 50 + 50

                                 = 100

b) 2 x 3 x 5 000 = (2 x 5 000) x 3

                          = 10 000 x 3

                          = 30 000

c) 9 x 13 + 9 x 7 = 9 x (13 + 7)

                          = 9 x 20

                          = 180