12*28=336

27*58=1566

39*600=23400

56*100=5600

36*59=2124

28*36=1008

k minh nha Băng Dao

12 x 28 = 336

27 x 58 = 1566

39 x 600 = 23400

56 x 100 = 5600

36 x 59 = 2124

28 x 36 = 1008

Bài 3 : 

A = 26 + 27 + 28 + 29 + 30 + 31 + 32 + 33

=> A = ( 33 + 26 ) . 8 : 2 = 236

Vậy A = 236

\(\text{#Hok tốt!}\)

a) 2 . 31 . 12 + 4 . 6 . 42 + 8 . 27 . 3 

 = 24 . 31 + 24 . 42 + 24 . 27

= 24 . ( 31 + 42 + 27 ) 

= 24 . 100

= 2400

SỐ ĐÓ LÀ 247

CẢM ƠN CÁC BẠN 

MÌNH MỚI BJ TRỪ 50 ĐIỂM XONG

CẢM ƠN TRƯỚC 

HIHIHI

SỐ ĐÓ LÀ

247

AI K MÌNH 

MÌNH K LẠI CHO

MÌNH THỀ

Bạn dựa vào công thức

a² - n² = (a + n)(a - n)

a) \(\frac{30}{51}\)\(-\)\(\frac{20}{52}\)\(+\)\(\frac{14}{34}-\frac{56}{91}-2\)

\(=\frac{10}{17}-\frac{5}{13}+\frac{7}{17}-\frac{8}{13}-2\)

= (\(\frac{10}{17}\)\(+\frac{7}{17}\)) \(-\)(\(\frac{5}{13}+\frac{8}{13}\)) \(-2\)

= \(1-1-2\)

=\(0-2\)

= -2

k cho mik nha

thank you bạn nhiều

tick mình đi

a) \(58+7x=100\)

\(=>7x=100-58\)

\(=>7x=42\)

\(=>x=42:7\)

\(=>x=6\)

b) \(3x-7=28\)

\(=>3x=28+7\)

\(=>3x=35\)

\(=>x=35:3\)

\(=>x=\dfrac{35}{3}\)

c) \(x-56:4=16\)

\(=>x-14=16\)

\(=>x=16+14\)

\(=>x=30\)

d) \(101+\left(36-4x\right)=105\)

\(=>36-4x=105-101\)

\(=>36-4x=4\)

\(=>4x=36-4\)

\(=>4x=32\)

\(=>x=32:4\)

\(=>x=8\)

e) \(\left(x-12\right):12=12\)

\(=>x-12=12.12\)

\(=>x-12=144\)

\(=>x=144-12\)

\(=>x=132\)

f) \(\left(3x-2^4\right).7^3=2.7^4\)

\(=>3x-2^4=2.7^4:7^3\)

\(=>3x-16=2.7=14\)

\(=>3x=14+16\)

\(=>3x=30\)

\(=>x=30:3\)

\(=>x=10\)

i) \(\left(10+2x\right).4^{2011}=4^{2013}\)

\(=>10+2x=4^{2013}:4^{2011}\)

\(=>10+2x=4^2=16\)

\(=>2x=16-10\)

\(=>2x=6\)

\(=>x=6:2\)

\(=>x=3\)

\(#WendyDang\)

b, Ta có: \(\dfrac{58}{53}>1>\dfrac{36}{55}\)

hay \(\dfrac{58}{53}>\dfrac{36}{55}\)

\(\Rightarrow0-\dfrac{58}{53}< 0-\dfrac{36}{55}\)

\(\Rightarrow\dfrac{-58}{53}< \dfrac{-36}{55}\)

Ta có : 

\(\frac{1}{21}+\frac{1}{28}+\frac{1}{36}+...+\frac{2}{x\left(x+1\right)}=\frac{2}{9}\) ( cái đề hình như có 1 phân số \(\frac{2}{9}\) đúng không bạn ) 

\(\Leftrightarrow\)\(\frac{2}{42}+\frac{2}{56}+\frac{2}{72}+...+\frac{2}{x\left(x+1\right)}=\frac{2}{9}\)

\(\Leftrightarrow\)\(2\left(\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+...+\frac{1}{x\left(x+1\right)}\right)=\frac{2}{9}\)

\(\Leftrightarrow\)\(\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+...+\frac{1}{x\left(x+1\right)}=\frac{1}{9}\)

\(\Leftrightarrow\)\(\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+...+\frac{1}{x\left(x+1\right)}=\frac{1}{9}\)

\(\Leftrightarrow\)\(\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+...+\frac{1}{x}-\frac{1}{x+1}=\frac{1}{9}\)

\(\Leftrightarrow\)\(\frac{1}{6}-\frac{1}{x+1}=\frac{1}{9}\)

\(\Leftrightarrow\)\(\frac{1}{x+1}=\frac{1}{6}-\frac{1}{9}\)

\(\Leftrightarrow\)\(\frac{1}{x+1}=\frac{1}{18}\)

\(\Leftrightarrow\)\(x+1=1:\frac{1}{18}\)

\(\Leftrightarrow\)\(x+1=18\)

\(\Leftrightarrow\)\(x=18-1\)

\(\Leftrightarrow\)\(x=17\)

Vậy \(x=17\)

Chúc bạn học tốt ~ 

fuck you